TrueRTA-for-dummies [Text View]

Ilkka

08-22-05, 05:19 PM

Since HTSpot transferred this quide into section where you have to be a paid member to get in, I decided to copy it here. Hope you'll all enjoy!

TrueRTA is a nice and small RTA-program (Real Time Analyzer) made by John Murphy. The free demo of the program can be downloaded from here (http://www.trueaudio.com/rta_down.htm). Unfortunately the demo is quite limited so you can't really use it efficiently. To make the most of it, you need to purchase an upgrade. True Audio offers four different upgrade levels from 1 to 4. I definitely recommend level 4, because this way you get the full 1/24 octave resolution, which is almost a MUST, especially if you are planning to some EQ'ing with BFD or similar. Level 4 retails $99.95, but it's all worth it. If you absolutely can't make it, take level 3, it comes with 1/6 octave resolution. Here (http://www.hometheaterspot.com/htsthreads/showflat.php/Cat/0/Number/729074/page/3/fpart/3/vc/1#729465) is a little proof why 1/24 is recommended.

Before anything, read the help files/topics, they are very helpful.

The program itself is very small (~1.4MB installed), but the project files are around 10MB each, so make sure you have atleast that much of free space on that drive.

1. What do we need?

-Computer/laptop equipped with a decent soundcard.
-Microphone (and preamp if needed).
-Some RCA cables between them.

Minimum System Requirements:
A 500 MHz Pentium III class PC with 64MB RAM running
Windows 98/ME/NT/ 2000/XP

Most modern soundcards will work just fine, for example almost any Soundblaster (Live, Audigy, Aydigy2 etc.) is fine. Soundcard must have line in and line-out connections. If you have some expensive soundcard, it will most probably work. Integrated soundcards like nVIDIA Soundstorm will work, but they are more difficult to calibrate, you need to set the input/output levels very carefully with them. I haven't yet seen a laptop with a decent soundcard. Most of them won't work. Use a USB or PCMCIA soundcards with laptops. For example M-Audio MobilePre USB is great. They retail around $100 - $150.

You can use the Radio Shack SPL meter as a microphone, but its accurancy is not very good. You can find few compensation charts for it, but none of them is perfect for your meter. They are just estimates. You can download the correction file from here (http://personal.inet.fi/private/ilkka/RS_calibrated.txt). NOTE: Check the end of this post, more info about RS. Save it as a text file along your other correction files (in "TrueRTA/Mic calibration files" folder). Frequency response of the RS meter limits up to around 10kHz (even with correction file). With the correction file it is reasonably accurate down to 15-16Hz. I personally have the older analog model, but the newer analog will work just fine. The digital version does not need any corrections when connceted from the output jack.

Much better choice is a Behringer ECM8000 microphone and a Behringer UB802 preamp/phamtom power. It's basically very flat even without any corrections, but here (http://personal.inet.fi/private/ilkka/BehringerECM8000corrections.txt) is a correction file for it too. Don't use the file that comes with TrueRTA. This better file is actually property of Edward Mullen (perfect for his mic), so everyone who's using this file, remember to thank Ed!

2. Calibration

First you have to make a simple loop from line out to line-in using the normal RCA cables and proper 1/8" connectors. You can just connect the other channel (use left) or both. Before you start the program, check your soundcard settings. Enter by double-clicking the speaker icon on the lower right corner of your desktop (if you can't see this, enter through control panel). In playback side all sliders except wave/mp3 and master volume should be muted. If you can't see the line-in slider, enable it through options/properties and mute it. This is crucial if you don't want to have some nasty microphone feedback. In recording side select line-in, if you can mute the others, do it. With most soundcards you can set all slider at full. If you have the nVIDIA Soundstream, set line-in slider at about 1/4. Now you can start the program itself.

By default the program is monitoring only the left channel, normally you don't have to change this. Now enter the "Audio I/O" menu and check that both sampling frequencies are set to 48 kHz. If your soundcard doesn't support these, use something lower for example 41 kHz. Now using the same menu, start "Sound System Calibration". Follow the instructions and you should see two lines on your screen. First a line something like this.
http://personal.inet.fi/private/ilkka/truerta/before_calibration.png
After a second or two the line should straighten up.
http://personal.inet.fi/private/ilkka/truerta/after_calibration.png
If the first line is not completely straight, lower the sliders like we learned before. If there is no line at all, check the connections. If you can't have a straight line, your soundcard is propably very cheap and will not work.

Now you can load the mic calibration file. Enter the same menu and "Open a mic calibration file". Select the correct file and open it. The range will throw you out, but use the buttons on the right side to make it readable (use around 0 dB - 120 db range). Now you should see a line like this.
http://personal.inet.fi/private/ilkka/truerta/mic_calibration.png
The absolute level (SPL's) might not be the same as in my picture. If you can't see the SPL readings, push down the SPL button. Notice that if you want to do the sound system calibration again, you have to unload the mic calibration file before doing it.

3. Connections

Unhook the loop at first.

If you have the RS meter: RS meter has an analog output using a single female RCA connector. Connect this into the line-in of your soundcard. Use proper adapter if needed. Connect both left and right channels from line out into your stereo system (usually pre/pro/amp). Use AUX/CD or similar analog inputs. Set your RS meter to C-weighting (very important, though some sources claim that output is not weighted, I will research this matter) and fast (actually fast or slow doesn't matter). Use the 80dB range. Make sure you have a fresh battery. Place the meter on a tripod or similar and point it towards the speakers. Place the tripod at the listening point (sweet spot, ear level).

If you have the ECM8000 or similar: You need an XLR cable (male/female) between the mic and the mixer. Mixer also supports 1/4" jack. Mixer output is either normal RCA or 1/4" jack. Check that microphone control knobs are near center, phantom ON, Main Mix around center. Output can be either Main Out, Ctrl Room Out or Tape Out.

4. Settings

When you have all the nessecary connections ready, we can look at some of the settings.
http://personal.inet.fi/private/ilkka/truerta/startscreen.png
This is the start screen of the TrueRTA. You can use either pink noise or quick sweep (QS) for measuring. If you have a proper mic, both ways will give very similar results. With RS meter the QS can be a little bit inaccurate at the lower end of the spectrum. The pink noise is more reliable, but also much slower.

Normally you should have the "L IN", "MIC CAL" and "SPL" buttons pushed down. "RTA Resolution" as high as you have purchased. "Speed Tradeoff" 20Hz. Averages 1. "Input/output sampling frequency" should be set to 48 kHz, if your soundcard supports them. Use lower if not. "CPU speed setting" anywhere you like.

5. Measuring

Select the "Pink N" from the left (Wave). Push the green "GO" button and you should see a wavering line like this.
http://personal.inet.fi/private/ilkka/truerta/noise.png
That is some backround noise of your room and also the noise from the whole measuring line. The lower the better. Now set averages 100 and the line should settle down. Averaging means that the program takes every 100th, or what ever number you have set, sample into account. John Murphy suggest a value over 1000, but I think it's too much. If you are using QS, averaging doesn't affect at all. Now you can push the Generator ON. Adjust the volume from your pre/pro/receiver so that the meter reads around 75 dB - 80 dB. It sounds quite loud, but it's not dangerous. Keep the noise running around 5-10 s so that the line settles down. Now you should see a line something like this.
http://personal.inet.fi/private/ilkka/truerta/fr.png

You can adjust the range if you want a closer look. This one is also smoothed, you can find the smooth option from the utilities menu.
http://personal.inet.fi/private/ilkka/truerta/fr_2.png

6. Advanced features

TrueRTA has an option to calibrate the absolute SPL level. Play for example 100Hz or higher sine wave (but below 500 Hz) and check the reading on your meter. You can play the tone using the built-in generator or you can use a cd/dvd. Have the program measuring all the time (GO button down) and enter Audio I/O / SPL Calibration menu and enter the SPL reading. Now the program is calibrated and it's showing absolute SPL's (=real). Notice that if you are playing a pink noise or similar wide band signal, you can see the real SPL level by pushing the dB button down. The line itself is at much lower level (~50 dB), but this is just because the nature of the signal. If you are measuring pure sine waves, the absolute level can be seen straight from the line itself.

Quick Sweep is a much quicker way, but I've noticed that sometimes the RS meter gives false readings especially at the lower end, since the sweep is so damn quick. You can make the sweep "slower" (actually it just sweeps narrower range) by lowering the input sampling frequency. I suggest 22.05kHz. If you set it too low (8kHz), your computer will slow down significantly. Pink noise is the "safe way".

You can also use Avia/DVE or similar disc for measuring. Find a suitable sweep (do not use single sine waves) and remember to have "PEAK HOLD" pushed down. Start the analyzator (GO) and start the sweep. Stop the analyzator (STOP) after the sweep and you should have the line on your screen.

Another cool feature is the Oscilloscope mode. You can easily check for example if your calibration signal is clipping or not. It's quite easy to use. Just have the signal running using the built-in generator and push the GO button (remember that you have to have the loop again). Adjust the range if you can't properly see the shape of the signal. Now you can set your levels very accurately. Just add the level (input/output sliders and Ampl. level) until the signal clips. Then back off by few dB until the signal doesn't clip anymore.

Here you can see a perfect waveform of a 1kHz signal.

http://personal.inet.fi/private/ilkka/truerta/1khz_signal.png

Here you can see the same signal, but now it's clipping heavily.

http://personal.inet.fi/private/ilkka/truerta/1khz_clipping.png

7. Quick recap

-Make a loop
-Run sound system calibration (adjust levels)
-Load the mic calibration file
-Connect the cables, line out -> receiver and mic -> line-in
-Calibrate absolute SPL if needed
-Measure your FR using either pink noise or QS

Copyright Ilkka Rissanen
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I must have forgotten something or maybe you didn't understand something. Please, post questions and I will make a small Q&A list out of them.

-------------------------------------------------------------------
Radio Shack SPL meter info:

Today I got my professionally calibrated microphone. Even without any correction files, it's only 0.5 dB off at 10 Hz. Pretty impressive. It was calibrated against B&K 4133 microphone.

I have now measured it against my analog RS meter. As I have said, the RCA output jack is weighted (C or A). But as Ethan showed, it appears that the output of the RCA jack of the digital RS meter is unweighted when set to C-weighting, when set to A, it's A-weighted. When set to C, it has a flat FR atleast down to 20 Hz.

Here is a TrueRTA screen of my results.

http://personal.inet.fi/private/ilkka/truerta/microphone_rs_comparison.png

As you can see, even with those general CFs, the RS meter is still below the true FR. It tracks the mic down to 40 Hz, but below that it's off. You need to compensate even more than for example 7.5 dB @ 20 Hz. Around 11.5 dB seems to be more closer. Of course every RS is different, so this might not apply to your RS. Although me and my friends have measured total of three RS meters (analog) and they all give pretty similar FR.

http://personal.inet.fi/private/ilkka/RS_calibrated.txt

Here is a calibration file which turns my RS into calibrated measurement microphone. When using this file its FR is within 1 dB (10 Hz - 200 Hz) from my calibrated microphone. It may not be as perfect with your RS, but much better than the general CFs. Notice that general CFs are way off below 15 Hz.

Analog version:
Use atleast general CFs or this (http://personal.inet.fi/private/ilkka/RS_calibrated.txt) file when measuring with the TrueRTA or smilar. Same thing if you are measuring manually (looking at the needle). You can use the rough corrections below, if you don't want to check the file (if you are measuring manually, add those corrections, do not subtract them).

Frequency / Correction
10 Hz +5 dB
12 Hz +6 dB
16 Hz +14.8 dB
20 Hz +11.5 dB
25 Hz +7.8 dB
30 Hz +5 dB
40 Hz +3.2 dB
50 Hz +2 dB
80 Hz +1 dB
100 Hz +1.2 dB

Digital:
Do not use any correction files when measuring with TrueRTA or similar. The output of the RCA jack is unweighted when set to C-weighting. When measuring manually, add corrections shown above to the readings.

Ilkka

08-22-05, 05:43 PM

Pictures of the connections (text/pictures property of Floyd Pierce) Thanks Floyd! :)

Note that I'm using a laptop so the Mic symbol would equate to line in with a normal sound card and the headphone symbol would equate to line out.

The loop connection for sound system calibration: (loop is just a stereo mini straight through)

http://www.hometheaterspot.com/html/spotadmin/uploads/loop.jpg

Radio Shack SPL Meter as Microphone:

http://www.hometheaterspot.com/html/spotadmin/uploads/RS_SPL_as_mic.jpg

Both hookups:

http://www.hometheaterspot.com/html/spotadmin/uploads/hookups.jpg

The more elaborate setup with a Behringer Mic and Mixing Console (provides phantom power to the Mic):

http://www.hometheaterspot.com/html/spotadmin/uploads/w-mic_and_pre-amp.jpg

The 2 following pics are a Closer look at Mixing Console connections:

http://www.hometheaterspot.com/html/spotadmin/uploads/mic_preamp.jpg

http://www.hometheaterspot.com/html/spotadmin/uploads/ub802.jpg

BradJudy

08-23-05, 03:21 PM

Excellent primer. Thanks for the work. Perhaps I'll add a bit on using ETF in a similar manner when I get the chance.

sholei

08-24-05, 01:24 PM

Thanks for the post, that is very helpful...
I think I am going to get the same software as you..

Brucemck2

08-28-05, 02:47 PM

Ilkka

08-29-05, 09:57 AM

On rec's from Forum members I've purchased TrueRTA and and an M-Audio FastTrack USB for the mic interface

http://www.m-audio.com/products/en_us/FastTrackUSB-main.html )

I'm still a bit unclear about how to set up the initial calibration loop for TrueRTA ...

I'll be using an outboard M-Audio FastTrack for the mic preamp and USB functionality.

FastTrack has mic input (XLR) and 1/4" input (for guitar or other line in.)

FastTrack has USB output and RCA stereo left and right outputs.

Laptop has USB port, mic input (tiny jack) and headphone output (tiny jack).

Two questions:

(1) in normal use (once all is calibrated) the proper setup is (a) mic into XLR input of FastTrack and (b) FastTrack into laptop via the USB port and (c) laptop headphone out into receiver's line in (for sending the pink noise, etc, signal to the speakers.)????

(2) in calibration loop/setup (a) headphone out from laptop into line in for the FastTrack and (b) USB from the FastTrack into the laptop via the USB port?????

Thanks!!!
Which microphone do you have?

To your questions: You have to forget the internal soundcard of the laptop.

(1) In normal use (once all is calibrated) the proper setup is (a) mic into XLR input or into line-in (1/4") of FastTrack and (b) FastTrack into laptop via the USB port and (c) Fastrack headphone out or Fastrack stereo RCA output into receiver's line-in (for sending the pink noise, etc, signal to the speakers.).

(2) In calibration loop/setup (a) from headphone out or stereo RCA output of Fastrack into XLR input or line-in (1/4") for the FastTrack and (b) USB from the FastTrack into the laptop via the USB port.

sholei

08-29-05, 11:44 AM

Hi,

I just purchased the TRUE RTA, and I have download it to my lap top. I need to get a mic now. I have the Radio shack analog SPL meter, but I want to get a better one. If I decided to get the Behringer Mic do I need to get the Mixing Console?
Can I just use the Mic only and plug it direct to the laptop?
may be I will get an adapter that will convert the XLR to RCA.
Or can I get a simpler mixer?

The mixing amp looks complicated, I don't even know what's all the button for.
is there a smaller version without all the buttons.
I want everything to be simple

thanks

Mario

BradJudy

08-29-05, 12:13 PM

You need a mic pre-amp with phantom power for the Behringer ECM8000. Your options include the mixing console shown above (there are a few different models) or a simple mic pre-amp like the Art MicroMix, Rolls (I forget the model number), etc. A basic mic pre-amp will run you about $50 and the mixing panel would run a bit more, but not much.

BradJudy

08-29-05, 12:16 PM

BTW: It also requires a soundcard that has a real stereo line-in which many notebooks lack.

noah katz

08-29-05, 01:34 PM

Can't he just use the RS meter's output jack and published calibration curves?

BradJudy

08-29-05, 02:55 PM

Yes, but since he asked about getting another one I gave him the important points. The RS meter could be used with the published calibration info and it would be reasonably accurate.

Brucemck2

08-29-05, 03:09 PM

Ilkka

08-29-05, 05:30 PM

Ikka ... Thanks!!! Your user guide was very helpful.

To answer your mic question: I'm using a five year old calibrated mic that came with my GoldLine 1/12th (low) 1/3rd (elsewhere) RTA

Had to replace the M-Audio FastTrack with a MobilePre. Salesman that pitched the FastTrack said they were "identical, except FastTrack was single channel rather than two channel". He was right, IF you ignore the phantom power differences!
Yep, Fast Track doesn't have a phantom power, so you can't use it for example with the ECM8000 (w/o an external power).

I think your mic is pretty good. Although calibration should be done every year, but it is still much better than say the RS meter.

Ilkka

08-29-05, 05:33 PM

MikeTz

08-30-05, 08:07 PM

Ilkka:

Thanks for the primer! When will you follow up with ETF for Dummies? :D

MT

Ilkka

08-31-05, 05:39 PM

Ilkka:

Thanks for the primer! When will you follow up with ETF for Dummies? :D

MT
Didn't BradJudy promised to do that one? :)

BradJudy

08-31-05, 06:11 PM

Didn't BradJudy promised to do that one? :)

I'll work on it once I have my mic back. I now have to different setups (one with a MobilePre and one with a separate mic pre-amp) so I can show two different connection setups. If I'm really feeling motivated, maybe I'll also work on one for the new R+D.

Grandarf

09-02-05, 12:37 AM

Nice thread! I didn't know you could connect the RS meter straight to a laptop!

I haven't yet seen a laptop with a decent soundcard. Most of them won't work. Use a USB or PCMCIA soundcards with laptops. For example M-Audio MobilePre USB is great. They retail around $100 - $150.

In the pics, you seem to be using your laptop, didn't you say that laptop soundcards are horrific and don't work very well?

I just purchased the TRUE RTA, and I have download it to my lap top. I need to get a mic now. I have the Radio shack analog SPL meter, but I want to get a better one. If I decided to get the Behringer Mic do I need to get the Mixing Console?
Yes, but since he asked about getting another one I gave him the important points. The RS meter could be used with the published calibration info and it would be reasonably accurate.

BTW: It also requires a soundcard that has a real stereo line-in which many notebooks lack.why would you need a stereo input if you're using one mic?

Ok, so I'm a bit confused now.. Laptop + RS meter, does this actually work? Or it depends on the stereo line in? (how can you know if it is?) And if it actually works, it works? No need for an external soundcard? (good quality?)

sholei

09-04-05, 11:27 AM

For the RS meter, doe it made a difference to use the digital or analog meter for the RTA software?
Will the reading be more accurate, if using the digital meter?

thanks

Ilkka

09-04-05, 01:17 PM

For the RS meter, doe it made a difference to use the digital or analog meter for the RTA software?
Will the reading be more accurate, if using the digital meter?

thanks
Check the end of my post. Some new info.

Ilkka

09-04-05, 01:29 PM

Nice thread! I didn't know you could connect the RS meter straight to a laptop!

In the pics, you seem to be using your laptop, didn't you say that laptop soundcards are horrific and don't work very well?

As I said, those are not my pics or my laptop. I just linked them.

I don't suggest using built-in soundcards (laptop or home PC). Usually they are crap. Use external soundcard, that is my adwise.

why would you need a stereo input if you're using one mic?

They are always stereo inputs.

Ok, so I'm a bit confused now.. Laptop + RS meter, does this actually work? Or it depends on the stereo line in? (how can you know if it is?) And if it actually works, it works? No need for an external soundcard? (good quality?)
It may work or it might not work. If it has a real line-in and line out connections, you have a chance. Make a loop and run a sound system calibration. If the first line is almost flat and the second (after calibration) is totally flat, it's working.

http://audio.rightmark.org/download.shtml

This is a good program (RMAA 5.5) which shows if your soundcard has a flat FR. It shows also THD, IMD, etc.

Jesse S

09-08-05, 01:00 AM

I get a large, narrow peak at 60hz using the rat shack meter to a soundblaster Live. Is this a ground loop? I never get ground loops from HTPC or dvd player on this system so I dunno why it's there. Not to mention the outlet there is only 2 prong (no ground, old house).

sethwas

09-08-05, 11:18 AM

Where was this months ago when I had to wing it to figure out how to use RTA ;)
The pics are especially helpful.

Seth

Kenrosencpa

09-12-05, 01:33 PM

The sound card on my Dell 700m didn't work so I picked up a Soundblaster Live USB and it worked fine.

I'm thinking about buying an ECM8000, I think the RS 4db correction discrepancy at 20hz is way too much and above 1k it looks almost useless. I have an older RS meter (probably more than 10 years old), it could even be further off. Has anyone used the Rolls MP13 microphone preamp? I wonder how it compares the the UB802.

Thanks

Kenrosencpa

09-12-05, 01:36 PM

Ilkka, What are the two sets of correction numbers starting at 515.625hz on you correction table?
thanks

BradJudy

09-12-05, 02:50 PM

Ken,

I haven't tried the Rolls, but I do have an ART MicroMix which is a single-channel mic pre-amp with phantom power and runs ~$50 from Sweetwater music. It works well. It isn't as flexible as a UB802, but it's very simple to use.

Ilkka

09-13-05, 01:34 PM

Ilkka, What are the two sets of correction numbers starting at 515.625hz on you correction table?
thanks
That second set is phase correction numbers for the RS. Numbers up from there are from the file which is available on the ETF site.

That ETF file doesn't have any corrections below that frequency, which is bad if your meters output is C-weighted or more (like mine). Digital version and some older analog versions output a flat signal, so for those the ETF file is pretty good.

Otherwise use my file.

Brucemck2

09-23-05, 06:00 PM

Does TrueRTA apply "C weighting" to the displayed data?

Reason for asking is that Room EQ Wizzard asks whether to correct for measurement devices's C weighting (when transferring data from TrueRTA to RoomEQwizzard.)

Thanks!

Ilkka

09-24-05, 08:13 PM

Does TrueRTA apply "C weighting" to the displayed data?
Of course it doesn't.

Reason for asking is that Room EQ Wizzard asks whether to correct for measurement devices's C weighting (when transferring data from TrueRTA to RoomEQwizzard.)

Thanks!
I wouldn't use this option unless you have a good C-weighted SPL meter. Radio Shack doesn't follow C-weighting. I would use the same correction file as in TrueRTA also in Room EQ Wizard.

But if you are transferring TrueRTA files, you don't need to apply any corrections, since TrueRTA has already corrected them once (don't do double).

Grandarf

09-25-05, 10:45 PM

Hey guys, i didn't get to try my lappy sound output to see if it worked, but there's a little gadget which might fix that problem:

I'm having a hard time finding it in Canada so I might have to order it directly from the site... Anyhow, I'll use it with optical to the Behringer DEQ Digital EQ, so the sound quality from the laptop will finally be top notch. (also ordered ECM-8000 mic) The USB 'sound adaptor' is only 30$, I think it should be superior to the laptop integrated soundcards...

Anyhow, I'll give an update if I find one, but it looks like it could be a very good solution if your laptop has a bad sound output. I know mine isn't very good, lot of interference from hardisk, its integrated DVDRom, etc.. its very noisy, I guess even with the analog from USB you wouldn't get any of that interference...

[edit] I just got it. Its really not very good with analog (noisy, moreso than my integrated laptop AC97!), and I can't get the digital output to work with my DEQ 2496 :(

donovanhebard

10-04-05, 09:12 PM

hi all,

just been playing with True RTA for a week or so, and this thread has been very helpful so far, so let me begin by thanking everyone for the great information.

i have a question, though. i am using an IBM ThankPad A30 laptop for the RTA, and was able to get the proper flattening second line on the RTA during the Sound System Calibration - however, if i run RTA with nothing plugged in to the sound card's ins or outs, i still get quite a bit of response on the SPL meter when i initiate the analyzer with "GO" button. there is also more "noise" present on the meter when using a mic than i would think is normal. is this indicative of power supply / hard disc noise? or perhaps of an inferior internal card?

i'm currently debating on whether to purchase an external sound card Soundblaster Live? or even maybe the M-Audio Duo USB or MobliePre USB (i am using the Behringer ECM800 mic).

i am using the RTA right now primarily to tune an automotive sound system with a 1/3 octave EQ - with mixed results so far.

thank you in advance for any thoughts, information, or advice, it is much appreciated.

-d

noah katz

10-18-05, 08:49 PM

Ilkka

10-20-05, 06:47 PM

Just noticed this:

The digital version does not need any corrections when connceted from the output jack."

That's great if true (I have one), but why would that be so?

Isn't the digital aspect just a different way of displaying the level from the same microphone?

Thanks
I don't know the reason, but I know atleast two occasions where a digital RS meter was compared to a Behringer ECM8000 mic and RS provided the exact FR without any CFs.

Ilkka

10-20-05, 06:51 PM

catapult

10-22-05, 01:44 PM

I don't know the reason, but I know atleast two occasions where a digital RS meter was compared to a Behringer ECM8000 mic and RS provided the exact FR without any CFs. I'd take that with a grain of salt. There have been a number of similar but different RS meters sold. The schematics of all the meters on Eric Wallin's mod page, two analog and one digital, all show the output jack tapping off after the A and C weighting filters. One easy way to tell would be to flip between the A and C settings on the meter with TrueRTA running. If the curve changes shape, the filters are being applied and you need a correction file.

Eric's page seems to be gone but here's the archive on the wayback machine.

http://web.archive.org/web/20041120043643/http://www.gti.net/wallin/rsmeter.htm

noah katz

10-22-05, 03:10 PM

Thanks, catapult.

Much to my shock, I read that I had sent Eric my very own RS meter!

So I guess I'm good to go :)

jplacson

12-07-05, 07:53 AM

I'm planning to purchase the Level 4 version of TrueRTA... does it come with more mic calibration files?

I'm using an M-Audio Firewire 410 w/ any of the following mics (so how do I calibrate any of them?)

Shure PG81
Shure SM94
Shure KSM 109

AKG CK98
AKG CK93

I live in the Philippines and I don't know anyone here who can calibrate microphones... so does anyone have cal files for any of these mics? Thanks!

Thomas-W

12-07-05, 01:59 PM

Those are all really nice general purpose recording mics, not test mics with flat FR. The Shure KSM 109 has reasonably flat response and goes lower than the rest.

Given your location it's going to cost you more money to get it calibrated, than it will to buy either the ECM-8000 or it's twin the Nady CM100.

J_Palmer_Cass

12-07-05, 02:40 PM

I'd take that with a grain of salt. There have been a number of similar but different RS meters sold. The schematics of all the meters on Eric Wallin's mod page, two analog and one digital, all show the output jack tapping off after the A and C weighting filters. One easy way to tell would be to flip between the A and C settings on the meter with TrueRTA running. If the curve changes shape, the filters are being applied and you need a correction file.

Eric's page seems to be gone but here's the archive on the wayback machine.

http://web.archive.org/web/20041120043643/http://www.gti.net/wallin/rsmeter.htm

I bought my RS Digital meter late last year, and the A and C scale does indeed change the shape of the curve with True RTA running.

The filters are being applied to my meter's output jack!

churchboy

12-09-05, 12:49 PM

Hi everyone, I am new here, what a great resource.
I just downloaded the trail version of Trueaudio RTA last night and I have a question. I conected a external sine wave generater (Rain Gain - 400hz @ 0dBu) into a channel on a Behringer UB802 mixer and ran the main out into the line-in on my internal sound card (Realtek AC97). I am trying to get familiar with the program and maybe I had something hooked up wrong. I wanted to measure the actual clipping point of the amplifier verses the indicaters on the mixer. The problem was the scope in RTA would show the signal clipping with the channel gain set almost to 0 and the faders at unity gain. Help?

jameswayneanders

03-10-06, 09:59 PM

I have downloaded the demo and when I start the software, I don't get any input response from the mic I am using. It is a condenser mic plugged into the M-Box which is plugged into the USB port. The input driver is RealTek AC97 Audio.

The Windows Sounds and Audio Devices properties only has one input driver and that is the RealTek driver.

Will this work? Or is there something else I need to do to get the software to recognize the audio input?

Thanks

Daniel.N

04-02-06, 12:48 PM

Interesting guide, thank you! I've been playing with this a little but can't get decent results; my S/N ratio is ~25dB at best, maybe that's why. The reason I can't get better S/N is that I check input signal from the SPL meter with the 'scope functionality to check for clipping.

Is that a reasonable thought, that if measuring a sine wave it should sort'a look like sine wave even after passing through the speakers and the mic? And also that if measuring pink noise, the scope should show no full amplitude samples? Or will measuring work even if the SPL meter seems to be outputting a square wave? :)

Thanks in advance!

DeCapo

04-17-06, 09:36 PM

Hi All,

I am considering using TrueRTA in conjunction with a laptop. However, I don't plan on using a mic. I would just like to use the line in/out's to take some frequency response measurements of some amplifier circuits I'm designing.

I was considering the SoundBlaster Extigy or the M-Audio MobilePre USB. Does anyone have any comments on either?

I noticed that some external soundcards seem to have a headphone output, but not a 'line out'. Can they be used interchangeably?

Are there any special features I should look for (or stay away from)?

Thanks!
-Dan

Nexus1

09-30-06, 08:23 PM

OK, I've tried three different external USB sound cards and none will give me a flat line when conducting a Sound System Calibration.

I broke down today and bought the Sound Blaster Live! 24-bit USB external sounds card thinking this would resolve the issue. Unfortunately, it didn’t. Everything is muted except for Wave out. What else could it be?

Kenrosencpa

09-30-06, 08:28 PM

Nexus1

10-01-06, 03:48 PM

Ken,

Thanks for the tip. I lowered the main volume and mic level to half and that did the trick. :D

Kenrosencpa

10-01-06, 03:52 PM

Ken,

Thanks for the tip. I lowered the main volume and mic level to half and that did the trick. :D
Hope you didn't buy those three sound cards :cool:

philip miller

11-14-06, 12:01 PM

tlparker

11-30-06, 03:44 PM

Don't know if anyone was aware of it or not, but "duhouse" on Ebay it trying to sell "valuable information", a big chunk of which is simply a URL that points to this thread.

I'm mentioning and including it here because all he's trying to do is make a fast buck off of public information posted on this site as well as public domain information (he doesn't even have the brains/cajones to copyright the two page word doc he sends you) and it made me sick.

I would question the legality of his trying to SELL a link to a thread on this site as something he has the rights to and can make money off of. If it isn't illegal, it's certainly wrong. He takes the "I have 25 years of experience in the field and this is valuable information that the average consumer should know about." If the "average consumer" can't find the info via a simple web search engine, then they're far too stupid to manipulate the parametric EQ settings in a Denon receiver. Good grief.

To top it off, in addition to mentioning download TrueRTA (I can't disagree there, I own the 1/24th octave version myself), he also includes the following Denon "tweaks":

AVR-3806 ‘Secret’ Installer Modes

IR (Infrared remote) Disable Mode

*
1) IR Disable Mode Setup is available only from the Front Panel (not by remote)

2) Enter into System Setup, select ‘6. Option Menu’, press ‘ENTER’

3)* Scroll down to ‘Exit’ (of Option Menu), then press and hold (for 3sec.) the cursor ‘left button’ when the cursor points*to "Exit"*of #6 Option Menu.

4) Remote Lock setup mode will be activated. Select*on/off by cursor left and right button

-In ‘Off’ Mode FL Display shows as following *Remote Lock*On / Off* : < Off

* -In ‘On’ Mode FL Display shows as following**Remote Lock On / Off* : > On

5) Press ‘ENTER’ button to exit this mode.

6) When this mode is ‘On’, and an IR*command is received, AVR will show "Remote Lock On" on the FL Display

*This caution also appears for the power on sequence and in status*mode*
check on the FL Display

7) Even if IR Lock mode is on, AVR will continue to accept serial 232 commands

Front Panel LockOut Mode

Two Different Lockout Modes are available:

All Controls (Buttons and Knobs) on the Front Panel

a. Start with unit in ‘Standby’ Mode

b. From the Front Panel, press and hold,*‘STANDARD’ and ‘INPUT MODE’ buttons and turn the Master AC power on

All Controls (Button and Knobs) on the Front Panel, EXCEPT Master Volume

c. Start with unit in ‘Standby’ Mode

d. From the Front Panel, press and hold, ‘STANDARD’ and ‘EXT.IN’ buttons and turn the Master AC power on
*
How to Defeat these modes:

From the Front Panel, press and hold* ‘STANDARD’ and ‘ANALOG’ buttons and turn the Master AC power on

When*each mode is ‘On’, and any button is pressed, AVR will show ‘Panel Lock On’ on the FL Display
*
*This caution also appears for the power on sequence and in status
mode*check on the FL Display

Even if Front Panel Lockout mode is on, AVR will continue to accept serial 232 protocol commands

**IR Disable and Panel Lockout Modes can be set*simultaneously or independently**

AVR-4306 ‘Secret’ Installer Modes

IR (Infrared remote) Disable Mode

*
1) IR Disable Mode Setup is available only from the Front Panel (not by remote)

2) Enter into system setup, select ‘6. Option Menu’, press ‘Enter’

3)* Scroll down to ‘Exit’ (of Option Menu), then press and hold (for 3sec.) the cursor ‘left button’ when the cursor points*to "Exit"*of #6 Option Menu.

4) Remote Lock setup mode will be activated. Select*on/off by cursor left and right button

-In ‘Off’ Mode FL Display shows as following *Remote Lock*On / Off* : < Off

* -In ‘On’ Mode FL Display shows as following**Remote Lock On / Off* : > On

5) Press ‘Enter’ button to exit this mode.

6) When this mode is ‘On’, and an IR*command is received, AVR will show "Remote Lock On" on the FL Display

*This caution also appears for the power on sequence and in status
mode*check on the FL Display

7) Even if IR Lock mode is on, AVR will continue to accept serial 232 commands

Front Panel LockOut Mode

Two Different Lockout Modes are available:

All Controls (Buttons and Knobs) on the Front Panel

e. From the Front Panel, press and hold,*‘DIRECT/STEREO’ and ‘INPUT MODE’ buttons and turn the Master AC power on

All Controls on the Front Panel, except Master Volume

f. From the Front Panel, press and hold, ‘DIRECT/STEREO’ and ‘EXT.IN’ buttons and turn the Master AC power on
*
How to Defeat these modes

From the Front Panel, press and hold* ‘DIRECT/STEREO’ and ‘Analog’ buttons and turn the Master AC power on

When*each mode is ‘On’, and any button is pressed, AVR will show ‘Panel Lock On’ on the FL Display
*
*This caution also appears for the power on sequence and in status
mode*check on the FL Display

Even if Front Panel Lockout mode is on, AVR will continue to accept serial 232 commands

**IR Disable and Panel Lockout Modes can be set*simultaneously or independently**

CSEmoses

12-01-06, 02:08 AM

OK, i downloaded and installed the demo of TrueRTA... i've a problem, simple i'm sure:

to quote:
"By default the program is monitoring only the left channel, normally you don't have to change this. Now enter the "Audio I/O" menu and check that both sampling frequencies are set to 48 kHz. If your soundcard doesn't support these, use something lower for example 41 kHz. Now using the same menu, start "Sound System Calibration". Follow the instructions and you should see two lines on your screen. First a line something like this."

OK, first of all... my soundcard input/output sampling frequencies can go up to 96khz, should i use that? or stick with the mentioned 48khz?
Second: where it says to use the same menu to start "sound system calibration" i do not have that in this menu. I've got "Line Input Calibration" and "line output calibration" only. Are these what is being referred to? When i click either of these, it is wanting me to get out a volt meter... which I so don't have. And hey, it doesn't include that in the list of 'what you need' in this guide for dummies either ;) so uh... that's where i'm stuck, for now. Do i need a volt meter? *confused* or am i looking in the wrong place?

FYI: My soundcard is an SB Audigy, i'm connecting an RS Analog Meter (33-4050) with an Stereo 1/8 to RCA-Y cable to the same jack on the back of the Audigy as my headset mic (unplugged while messing with TrueRTA of course, no splitter there).
... I'm short on cables. Going to hit radio shack (source by circuit city here in canada) and buy some tomorrow, so i can actually get some measurements done.

Thanks a TON for any help you can provide, as i'm REALLY new at using this software, and audio 'tweaking' in general. ... Though i'm not a computer newbie, not at all, so that should help in the learning curve with this really thorough looking application!

Red GTI VR6

12-15-06, 03:23 PM

Here's a screen shot of the menu as it should be and where the Sound System Calibration is listed. Hope it helps!

Red GTI VR6

12-15-06, 03:55 PM

tlparker

12-15-06, 09:01 PM

One quick question, when doing the first part of the calibration, should the graph be in relative mode?

When I'm calibrating, if I don't have it set to relative mode, I don't get the flat line. If I have relative mode turned on, I get the flat line. In my case, at a 69.5 dB.

Is this correct?

Otherwise, it's really jaggid.

Also, should I be using a mono cable, or a stereo cable to link the two? Does it make a difference?

This is all on this card: http://www.auzentech.com/site/products/x-meridian.php

With Burr Brown opamps.

Thanks!

I'd be curious as to anyone's impressions or experiences with this card, in particular as it compares to the m-audio Revolution 7.1 and/or Audiophile 192 (both of which I have). I've got mixed feelings about both of my m-audio cards. When the 7.1 card is working, everything sounds fantastic, but then there are moments when it takes up so much cpu (I have a 2.4ghz p5) that during some heavy disk access times it can choke or stutter during playback of files. I also don't care for the 7.1's connectors (one coax digital I/O, which is great as optical stinks), but all the rest are mini jacks that you use mini to 2-rca cables for connections, and that really stinks. The audiophile 192 is a fantastic card, particularly for bringing in analog audio at the very highest quality (with XLR connections, monitor connections, etc., via a small extension multi-connector), but that's about it. I'd like to find one card that does both, I'm wondering if this is the card??

Red GTI VR6

12-16-06, 09:58 AM

I'd be curious as to anyone's impressions or experiences with this card, in particular as it compares to the m-audio Revolution 7.1 and/or Audiophile 192 (both of which I have).

I cannot help you there, sorry. I've not listened to either of those cards. In fact, I haven't even listened to this card yet...lol I'm still in the process of making a bunch of modifications.

mini jacks that you use mini to 2-rca cables for connections, and that really stinks.

I agree, I really wish these cards would come with RCA outputs. Because of that, I'm modifying my card: http://www.mp3car.com/vbulletin/showthread.php?p=979552

I'd like to find one card that does both, I'm wondering if this is the card??

I cannot comment on the 7.1 features of this card as I'm not interested in using them. I'm using this card in my car for stereo play back. If for some reason, this set-up doesn't work, I'll be throwing this card in the home theater PC/system that we are starting to build and go with something like Mark Of The Unicorn UltraLite (http://www.motu.com/products/motuaudio/ultralite/)

Istari1

12-18-06, 05:38 PM

Good stuff. . .I sense myself going out and buying a new mic, meter, and TrueRTA. . . damn you all ;)

Vidfreaky

12-19-06, 09:49 PM

Hey guys, I've got the 1/3 octave version of True RTA (just thought I'd try it with more than just the 1 octave version before upgrading) and I'm using the Edirol UA-25 as a soundcard for my laptop.

I've connected the L RCA out to the L 1/4" in. Everything's set at 48KHz. The output pot is cranked and the input pot is at 12 o'clock on the edirol. I can't use the "sound system calibration" as it is greyed out on the menu so I can't click on it. I see it, it's there, just not active. How do I activate it?

cacin

12-23-06, 11:52 AM

How would you do your setup if you're using the software with laptop in a car? Where do you connect the line in and line out from the soundcard?

208

12-26-06, 07:16 PM

The sound system calibration is grey'd out on mine also. Do I need to upgrade to a higher level in order to activate it, or am I missing something?

208

01-02-07, 12:04 PM

OK, I answered my own question. Just upgraded to level 4 and every function is now available. Just goes to show you that you get what you pay for!

mpsmps

01-08-07, 11:12 PM

I'm not able to get a reasonable calibration on my Dell 300m laptopwith either my PCMCIA Audigy 2 ZS (even following the Audigy instructions mentioned in the TrueRTA FAQ) or with the integrated audio. What soundcards have people used successfully with their laptops?

Thanks,

Mike

mpsmps

01-09-07, 04:49 PM

I have completed purchase and installed Level 4 of RTA and, using a Behringer 8000 microphone along with a Soundblaster Live USB card on my pc, I began taking measurements of my room. The response graph that I end up with has various steep vertical spikes, for want of a better term, throughout the range. What am I likely to be doing wrong. Thanks in advance for your help. Phil Miller
Hi Philip,
Creative automatically maps the line-out into the line-in for game effects. If you go to the FAQ on the TruRTA website, you'll see a question about calibrating with the Audigy containing directions on how to fix that problem.

Mike

wiz561

01-17-07, 02:06 PM

Quick Question... TrueRTA looks like something I am looking for. But once you get done running all of the tests as outlined in the first post, what do you do next?

As you can tell, I'm just trying to learn about this. I'm guessing that you want to adjust your equalizer so that dB SPL is 'flat' across all frequencies when it does the sweep. By flat, I mean as flat as possible. At this point, everything is correctly adjusted.

Am I on the right path or WAY OUT in left field?

Thanks!

josh1233

01-17-07, 03:33 PM

I've been thinking about getting the TrueRTA for a while (I have an old Audio Control RTA and a Coustic RTA). I am wondering what cables I would need if I am going to use the M-Audio MobilePre USB Portable Audio Interface and the Behringer ECM8000 Microphone with TrueRTA and a laptop?

- I guess I would need a XLR (1 male end/1 female end) to run from the mic to the preamp.
- USB cable to run from the laptop to the preamp.
- mini headphone jack on both ends to run from the stereo mic input to the stereo line output on the MobilePre for calibration?
- and what cables to run out of the MobilePre to the amp (dual RCA and the other end 1/4" jack?)

help would be greatly appreciated,
Josh

josh1233

01-17-07, 04:10 PM

donovanhebard, did you get your issues worked out?

When setting up the audio system in a car, you should EQ each side of the car separately (provided your EQ has separate adjustments for right and left and you are trying to get the car to sound good from both the driver and passenger side). After the initial setup of each channel, check both together (stereo). Do not boost any frequencies when adjusting both channels together, only cut frequencies. Try using both correlated and uncorrelated pink noise when EQing each channel separately and together. Set the EQ at an average between the 2. Do a lot of listening to well recorded audio tracks between EQing (like something from Sheffield Labs). And don't try to go for a flat (straight line) curve. Just get rid of peeks and dips. To do this properly, it will take a lot of time over the course of a week or two, depending on how flexible your processors are.

Before you do any of this you should set your gains from each piece so that the signal does not clip, then when you get to the amp(s), set the max amp gain to a 3:1. In other words, set the amp gain to just below clipping, read the voltage, then multiply that by three and set the amp gain to that, then cut the gains from amp to amp to balance the sound. Also, the xover points and slopes should be set before EQing to get the car sounding as good as possible. The EQ is only used to smooth thing out.

Also, make sure that, if you have time delays, they are turned off before EQing the car (they should be the last thing set). You will probably end up with a small dip at 250hz-400hz that can not be entirely corrected (if you are running speakers in the doors).
*Kick panels would be better to eliminate cancellation, would widen the sound stage, and decrease the path length differences of the right and left channel.

Another trick that may help, before eqing. If your sound stage is low, try reversing the polarity of one channels tweeter and the other channels mid. I know it sound wrong, but it usually bumps the image up about a foot. And with the amount of reflection points in the car audio environment, it will most likely focus the image better and you should not notice any loss in the mid-mid bass range that one would expect from doing this. Also, it should help the center image from both the right and left seating positions.

WSLam

01-30-07, 04:24 PM

Does anyone know how to create a 'loop' for the Apogee Mini DAC and Mini ME? I am using an ECM8000 and have the Apogee combo, but I can't figure out how to get it to work! Can anyone help? Thanks.

tsound

02-01-07, 12:59 AM

jaegertc

02-20-07, 03:31 PM

I have a problem with TrueRTA when used with a Soundblaster Live! 24 USB. The program crashes after pushing the "Stop" button. It starts fine, the tone generator works fine, but as soon as "Stop" is pressed the program crashes. Anyone seen this before?

tsound

If you haven't, try the REW/BFD forums at HomeTheaterShack.com. They have several threads dedicated to REW (and RTA?) and at least one to getting room eq software to work nicely with that soundcard.

audiozealot

03-19-07, 02:44 PM

Is there a way to splice together 2 graphs in TrueRTA? I am trying to splice together a near field measurement of the woofer with a far field measurement for a better representation of the frequency response of a speaker. I see how to shift the curves but is there a way to delete the unwanted pieces of the curves at let's say 300Hz? Please don't make me go into Paintbrush and delete pixels :rolleyes:

Thomas-W

03-20-07, 08:20 PM

You can't splice but if you save each one to a different memory setting, you'll see the two plots combined.

andybdjuk

03-22-07, 04:39 PM

Hi guy's I have read all the post and hope I have not missed the answer to my question. I have an M-Audio USB Portable Audio Interface and the Behringer ECM8000 Microphone with TrueRTA and a laptop?

I set it up last night in my club to monitor the SPL across the spectrum of a band that was playing.

I have cal'ed the interface flat but later noticed that the clip light was coming on. Turning down the input gain obviously changes the SPL graph. Could somebody give me any pointers and what I am doing wrong? And how I set it up correctly

Thanks in anticipation

Andy

karos

04-22-07, 09:21 AM

how is trueRTA different from RoomEQ? Isnt it the same author?

sorry-I just notice that one is John Murphy the other is John Mulcahy. But how are these apps different?

jonleelk

04-23-07, 07:48 AM

Just set up TrueRTA on my acer laptop equipped with onboard Realtek HD audio. The FR for the realtek is quite bad, started to slop down from 100Hz downwards. However, TrueRTA was able to equalised to a almost flat line when using calibrating sound card option.

Is this result accurate enough to use, or should I add an external PCMCIA Sound Blaster® Audigy® 2 ZS Notebook which is supposed to have a Frequency Response (+/-3dB, 24-bit/96kHz input) = <10Hz to 46kHz (2V Rated Output)hae a FR of +1 3dB

taiguy

04-26-07, 02:03 AM

I've got a Behringer ECM8000 microphone running to a Mackie 1202-VLZ mixer/preamp to Audigy 2 ZS notebook. I tried following the directions in the pdf file off of TrueRTA's website but they're for an older version of the creative software and I can't find the same options available. It shows in my sound system calibration test. Can anybody please explain in detail how they got their Audigy 2 ZS card to work properly with TrueRTA? Thanks.

mitchlampert

04-26-07, 01:09 PM

Will True RTA run on Windows Vista?

catapult

04-26-07, 01:56 PM

scotland60bwork

05-17-07, 04:21 PM

Hi all -

I have TrueRTA full, ECM8000 mic, MobilePre USB, and the digital RS SPL meter. I've downloaded all cal files from this site. I perform the sound card cal with a loop from the line out 1/8" jack to the ch1/line 1/4" jack with adapter. I am able to get a flat line and do not appear to get any clipping. In the MobilePre audio control panel in Windows, I have the USB Record and Output sliders maxed and the monitor slider muted. Additionally, I keep the knobs on the front of the MobilePre at midposition.

After sound card cal, I hook up the SPL meter to ch1/Line and perform the absolute SPL cal, with the RS SPL meter cal file in use. This appears to work well. However, when I then proceed to hook up my ECM8000 and change the cal file to the ECM8000 file I got from this site, the SPLs appear to be pretty far off, usually about 5-10 dB difference.

I also set up the SPL meter on ch1 and the ECM8000 on ch2 and I have the same problem, even if I change the cal files. I find it hard to believe the cal files would be so far off.

Is there something that I'm missing?

Please help!

Cheers
Scot

Richard Mayer

05-21-07, 07:57 PM

scotland60bwork

05-22-07, 03:39 AM

Thanks Richard!

I was able to calibrate the SPL by holding the RS meter right next to the ECM8k. I just didn't know whether this was a valid method of calibrating it or not, and wondered what the reason was for the difference. I guess this is the only way I can do it then. Thanks for the help!

JimP

06-06-07, 12:03 PM

Will True RTA run on Windows Vista?

Does anyone know??

DrFeelgood

06-14-07, 12:39 PM

Hi there - newbie to all this very technical stuff, and come from the world of ICE :)

Could someone hold my hand, and walk me through the most simple setup of TrueRTA? At present, I'm only using it for spectrum analysis in a car for the purposes of equalisation/crossover setting. I thought I'd better get that confession out of the way first :redface: I promise to learn more of its features later! The kit seems to be the standard recommended stuff from reading this thread - ie laptop, M-audio mobile pre and a Behringer ECM8000. I got lost when you reached the word loop...

Many thanks!

Richard

eugovector

06-14-07, 01:07 PM

mitchlampert

06-14-07, 01:35 PM

Will True RTA run on Windows Vista?

Yes it will but the drivers for the M-Audio will not. So I had to use an older laptop to get it running.

mitchlampert

06-14-07, 01:39 PM

One more question. Can I use the pink noise generator in my processor for the tone or do I have to use the tone generator in the RTA program?

freythman

06-23-07, 12:00 AM

Has anyone had experience with the Alesis MultiMix 8USB Mixer? It's the same price as the M-Audio MobilePre, except its an 8 channel mixer with 4 XLR inputs, each with phantom power. It just seems like I'd be getting more bang for my buck...

Here's what I'm considering for my RTA techie package:

TrueRTA Level 4 (no brainer)
Behringer ECM8000
Either: MobilePre OR Alesis Multimix

Calvary

07-14-07, 11:16 AM

Good Day All,

I have read all the replies on this thread and have found it quite interesting. I will admit that I am brand spanking new to this so I apolozige if my questions seem to waste your time.

My church santcuary is in an industrial warehousing unit that is a 50'W x 50'L x 24'H. We have flat surfaces all over the place (all of the walls are drywalled with no insulation, the roof is corrugated metal with trusses, the floor is concrete covered with industrial carpet)
The dimensions and physical properties of the room make it a real challenge to get "proper" sound. I am investigating several methods of sound treatment, however I would also like to tune the room.

Question: Will TrueRTA work for a room this large? I am looking to purchase the M-Audio Mobilepre and the Behringer ECM8000 along with a Radio Shack SPL meter. ---> are these compenents suitable for tuning and profiling my santuary? Would I the church mixer in this setup?

Thanks in advance.

Rayjr

07-21-07, 11:45 AM

Hello all
I was wondering if TrueRTA can do energy time graphs.

Thanks
RayJr

DrFeelgood

07-25-07, 02:33 PM

Evening! I'm still struggling....:shake:

I've connected the MobilePre USB each and every way I can trying to setup the loop, but can't get a proper trace. Could someone take pity on me and walk me through it? tia!

Kal Rubinson

07-25-07, 03:06 PM

Hello all
I was wondering if TrueRTA can do energy time graphs.

Thanks
RayJrNot that I've seen. You need different software for that.

Rayjr

08-08-07, 10:09 PM

Not that I've seen. You need different software for that.

Kal
What software do you recommend for doing Energy time graphs......I have been useing a borrowed Sencore sp295..but would like to know what else is out there?

RayJr

Kal Rubinson

08-08-07, 10:13 PM

Room EQ Wizard, ETF, TEF in order of sophistication, complexity and cost. There are others but these are the 3 I know.

SierraMikeBravo

08-11-07, 08:38 PM

Hey all!

Well, just got done using the true rta fir the first time. I have one question. For some reason, I could not get the pink noise graph to get to 70 dB or higher. My entire graph was hovering around 50-60 dB no matter how much how much I increased the gain on my Denon 4306. As a comparison, I used a SPL to see if I was in the ballpark. The SPL showed 80-90 dB while the true rta showed only 50-60. Is this normal? However, when I used a since wave tone of 200 Hz, it spiked up to around 80 dB on the true rta with no increase in gain on the receiver. I used that as the reference, but is it in the nature of the pink noise signal to display that low on the rta? Doesn't make sense. The loop was fine and flat lined around 105 dB. Anyone know what may be the issue? I am using a ECM 8000 mike with the calibration file from tru rta. Also, and M-Audio PreUSB. I had the "R in" button pressed for the RTA as I using right input and outputs. I

Thanks a bunch!
Shawn

IncraTL

08-22-07, 08:35 PM

Hi:
Thanks for the RTA info . It's well written and detailed and will be quite helpful to me.
Just a quick question, if you don't mind -
I tried to download the free Level 1 RTA and was told I couldn't because my Dell has a Vista operating system. O.K. On 4 December 2006, my father-in-law purchased a level 4 RTA disk, (Version 3), as a Christmas present for me.
Question: Could I use this Level 4 disk on my Dell, (w/ Vista)?

Thanks for your time with this,

George

tonyptony

09-01-07, 08:18 AM

I just ordered TrueRTA via credit card for direct download. How long does it take for the process to complete? That is, once I order, how long till I get it?

Kenrosencpa

09-01-07, 10:53 AM

Their website say's up to 12 hours. This is a holiday weekend maybe more or less

AAR

09-26-07, 06:34 PM

I am a relatively new user of TrueRTA.

The program indicates that the impulse wave is used for "delay testing", yet I cannot find any documentation in the help file as to how to do this. I want to time align (as best possible) the two drivers in a two-way system. Is there a way to derive the step response??

TIA

AAR

bgavin

11-11-07, 11:56 AM

I have found a show-stopper bug in TrueRTA at v3.3.3.

During bass horn testing, I was having data anomalies. As it turns out, TrueRTA is broken. Very repeatably broken.

1 - The program SPL meter does not agree with the captured data points

We measured a Tuba 36S at 1w/1m, and expected 105 SPL. The RTA meter display read 106+, and the peak data point read 105. At first we figured the programm was summing all the data under the curve, not just the peak value.

Bug.

2 - The data export function is entirely corrupt and useless.

I was having erratic results using the Workbench to export data. We use this function to sample 100 Hz as a reference point. We then sample Pink noise and export the data. The Pink data points are increased where 100 Hz matches the sine wave sample. The data are wrong.

Every time I export data, the .TXT file data points change by approximately 2dB. Reimporting the same data points into Workbench raises the graph 2dB. Exporting the same data raises it again, reimporting raises it yet again.

Bug. The exported data points are entirely useless.

I have notified TrueRTA this is a show stopper bug.

bgavin

11-14-07, 11:42 AM

I called TrueAudio this morning and spoke with Sharon. My email to Support from 11/11 was still sitting in queue, unread. She forwarded the mail to John Murphy along with screen shots and bug attachments. I asked for a confirmation of receipt, so I know he got it.

As usual, she was in denial about there being a bug. As a 35 year veteran of software development, I expected this. I won't accept it, but denial was expected. What is more important is what John Murphy has to say about the bug, and how soon he fixes it.

I build bass horns and pro sound cabs, and the TrueRTA bug has invalidated my measurements. The curve shapes are correct, but the SPL values are all corrupt. Many days of accumulated measurement data are worthless.

John L. Murphy

11-16-07, 11:31 AM

Hello TrueRTA users!

bgavin reports 2 bugs which I would like to address:

My Summary:

Bug 1: appears to not be a bug at all but just a normal measurement difference.

Bug 2: appears to be valid but is limited to affecting only imported .txt data.

Let me explain:

Bug 1
bgavin reports:
<< 1 - The program SPL meter does not agree with the captured data points

We measured a Tuba 36S at 1w/1m, and expected 105 SPL. The RTA meter display read 106+, and the peak data point read 105. At first we figured the programm was summing all the data under the curve, not just the peak value. >>

This is not a bug, just perhaps an unexpected result. TrueRTA is giving correct readings for both the broadband dB level and the individual narrow-band dB level because these are actually two different measurements. Look at it this way; the narrow-band dB reading will always be lower than the broadband dB level because only the level of one individual frequency "bin" is represented by an individual bar's cursor readout (or exported data point). The broadband dB level (the bar at the far left) represents the energy present in the full frequency spectrum which includes the frequency bin of interest along with all the other frequency bins. Even if the one bin is at, say 105 dB SPL, and the other bins are all at some lower (noise floor or distortion) level the broadband dB SPL reading (as indicated by the large bar at the far left of the plot area and by the on screen numeric display at the top left) will measure at some higher level due to the broadband background noise. This is normal for these types of measurements. Only in the theoretical case where the distortion and noise were infinitely low would the two measurements be the same. For real world measurements there will always be a difference.

Bug 2
bgavin reports:
<< 2 - The data export function is entirely corrupt and useless.
...Every time I export data, the .TXT file data points change by approximately 2dB. Reimporting the same data points into Workbench raises the graph 2dB. Exporting the same data raises it again, reimporting raises it yet again. >>

The data export function actually works just fine. If you have 240 bars of onscreen data you will get 240 data points when you export the data to a .txt file. If you inspect the file you will see that the data points precisely match the individual on-screen bar levels. Your exported data is fine.

However, I have confirmed a problem with data import from .txt files that would explain the reported error. While the exported data precisely matches the on-screen bar readouts, some types of data can be shifted as much as a couple of dB upon import. This shift is most likely related to the way imported .txt data is interpolated into the (much larger) internal data buffers. While a response is represented by about 240 data points on-screen or as an exported .txt file the full data set actually consists of about 32,000 data points. When you save your files in project files (.rta) or single sweep files (.rt1) you are saving and restoring the full 32,000 data points. When data is imported from .txt files it has to be interpolated into the 32,000 data points. Some loss of resolution is to be expected but I think it can be improved. Smooth, broad responses seem to be minimally affected while narrow band measurements (such as single tones) are affected the most.

The screen shot below shows the difference between measured data and the same data data exported/imported to/from a .txt file:

http://www.trueaudio.com/images/text import error.jpg

I will investigate this .txt data import anomaly and address it in the next release of TrueRTA. In the mean time it is fortunate that most users do not normally export and import their data. As long as you are storing your data in the normal TrueRTA project file format (filename.rta) or even exporting to single memory files (filename.rt1) you should not be affected by this bug. Again, only data imported from .txt files appears to be affected.

Regards,

John

bgavin

11-18-07, 05:39 PM

This is not a bug, just perhaps an unexpected result.

I am a 33+ years professional programmer, and the corollary to this is “a feature is a bug with useful side effects.” This is the sort of denial one expects from Microsoft. It does nothing to correct the problem, so let's please stay focused on the bug.

Here’s the first problem restated:
1) TRTA geneartes a 100 Hz sine wave
2) Separate SPL meter reads 105 SPL
3) TRTA on-screen meter reads 106 SPL
4) TRTA on-screen data point reads 105 SPL
5) Export to TXT shows 100 Hz at 105 SPL

This is a point measurement, not broad band. The sine wave is 40dB higher than background. If TRTA is accumulating across the entire spectrum, it is still hearing 100 Hz at 40dB higher intensity than background.

I always calibrate TRTA to the SPL meter.
Do I calibrate TRTA to the Screen data point, or Screen Meter value?
Question: one is wrong, one is correct. Which one?

I calibrate TRTA to the SPL meter with the screen data point. I do this because the exported TXT data point agrees with the SPL meter. I treat the Screen Meter as wrong, because it does not agree with the data points.

The meter issue is mildly annoying but certainly not a show stopper.

*************

Here is the show stopper bug:

However, I have confirmed a problem with data import from .txt files that would explain the reported error. While the exported data precisely matches the on-screen bar readouts, some types of data can be shifted as much as a couple of dB upon import.

This is the entire crux of my bug report.
This effect is cumulative, and completely invalidates my test data.
Each export/import of the same data changes the TXT file and the screen data points.

I require ACCURATE data in the import/export function, so “shifted as much as a couple of dB upon import” is not at all acceptable for my needs.

All of my measurement work centers around the TXT data points.

When data is imported from .txt files it has to be interpolated into the 32,000 data points. Some loss of resolution is to be expected but I think it can be improved.

Any loss of resolution for the known TXT data points is not acceptable.

Here is the bug fix: Interpolate the intermediary points between the known TXT data points. After interpolation, verify the results with the TXT points to insure there is no change to the known values.

I would be happy to be your early tester for the resolution of this bug. I cannot wait a year, or whatever, for the next release. If my schedule does not fit yours, I will contact you for a refund, and find a different measuring tool.

bgavin

11-23-07, 09:30 PM

I have found a critical data error bug in the Level 4 TrueRTA v3.3.3 RTA Octave Resolution display.

The on-screen and exported data points are invalid for all resolutions lower than 1/24 octave.

The user takes a measurement which is present in the Workbench.
When the user selects different RTA Resolution, i.e. 1/3 Octave, 1/6 Octave, the data values change.

The measurement has not changed. TrueRTA is changing the data point SPL values as it changes octave resolution.

This is dead wrong.

The bug is demonstrated by using 80 Hz as the sample frequency because 80 Hz is present in all octave resolutions except for 1 Octave.

In this example, a 100 Hz sine wave measurement was taken at 1/24 octave resolution.
Below are the results at 80 Hz.

1/24 Octave: 35.22 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-24_Resolution.jpg)
1/12 Octave: 38.11 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-12_Resolution.jpg)
1/06 Octave: 40.66 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-06_Resolution.jpg)
1/03 Octave: 43.95 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-03_Resolution.jpg)
1/01 Octave: 50.47 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-01_Resolution.jpg)

Exporting the Workbench verifies the onscreen dB values match the text file data.
The 1-octave resolution does not export 80 Hz, so only the screen point was used.

Every SPL data point on both on-screen and exported values are corrupt at all resolutions lower than 1/24.

bgavin

11-24-07, 12:59 AM

I have found a horrific data portability bug in the Level 4 TrueRTA v3.3.3 RTA.

Transferring the .RTA file from the Measurement laptop to my Office workstation results in corrupted data.

Example:
I spend a whole day taking measurements in the field with my laptop.
When I get home, I transfer all .RTA files to my primary workstation.
I load these files into the identical version of TRTA.

AND ALL THE DATA IS WRONG!!!!!!!!!!!!!

Every single SPL data point is off by approximately -8 to -9dB.

Laptop Trace (http://www.bgavinsound.com/reference/music/test%20results/TrueRTA%20Bugs/Portability%20Bug/Laptop_Trace.jpg)
Desktop Trace (http://www.bgavinsound.com/reference/music/test%20results/TrueRTA%20Bugs/Portability%20Bug/Desktop_Trace.jpg)

I wondered why I was losing day after day of field test data. Transferring it to my workstation produces these horrific errors. When I export the files to TEXT, it verifies the data corruption.

This is seriously, seriously lame.
This bug is akin to creating an Excel 2003 sheet at the office, and finding it corrupt on the home version of Excel 2003. This bug makes my TrueRTA data useless on any machine other than the one it was created on.

jonash72

11-27-07, 10:52 AM

I have a weird issue with my new Laptop and True RTA.

Setup is as follows

Laptop: Compaq nx7300 with Windows Vista installed
Soundcard: M-Audio USB Mobile Pre

I try to do a system Calibration, but I just cant get it to do a correction worth it's meaning.

On my stationary PC, I have Windows XP, and when I try it there with the same soundcard, the same settings, I get a ruler flat line. I move the USB cable over to the Laptop, without doing anything else, and perform a sound cal and it looks nasty. Specifically from say 500Hz and down.

Any ideas?

The things I can think of myself are:

1. Could it be the M-Audio driver for Windows Vista?
2. Could it be the Laptop itself, the USB port or some such?

Any help appreciated.

(I have been thinking about installing XP on the Laptop as well, just to remove one of the "unknown" an dsee if that helps, but I'd rather discuss other options before I do that, obviously...)

Thanks,
Jonas

carbuff

11-27-07, 11:23 AM

I have a weird issue with my new Laptop and True RTA.

Setup is as follows

Laptop: Compaq nx7300 with Windows Vista installed
Soundcard: M-Audio USB Mobile Pre

Jonas,

I'm having a very similar problem, you beat me to posting about it. :)

I have a MobilePre with a Behringer mic. Using either the built-in soundcard or a cheap USB unit that I purchased, I can get flat calibrations. With the MobilePre, I'm not getting a flat calibration. And when I take measurements, whether using the calibration or not, I have huge spikes and peaks (which of course is possible from the room, but moving the mic doesn't help much), so I'm not trusting the results I see.

I'm running Windows XP on my laptop (older Dell unit).

I have another question along these lines also...

I don't use an analog source. I'm using the DACs in the Cary 11a unit that I have to produce all output to my amp. So, in this case, I'm not sure that doing a calibration makes any sense at all? Since I don't care what the analog out side of my soundcard is doing, testing and calibrating a loop doesn't make a lot of sense?

So I've been experimenting with a few things to see what I can do. From my laptop I can drive a digital coax connection to my preamp. So, I have been trying to use trueRTA to calibrate by driving digital into the preamp, and connecting the line-in of my soundcard (any of the 3 I have) to the left channel output of the preamp. In my mind that seems like the starting point that I would want to calibrate, since all of my sources are digital?

Does that approach make sense?

If so, it's not working any better than my above scenario in the sense that I can't get a smooth calibration with this setup either...

Any helpful suggestions appreciated!

jonash72

11-27-07, 12:10 PM

Jonas,

I'm having a very similar problem, you beat me to posting about it. :)

I have a MobilePre with a Behringer mic. Using either the built-in soundcard or a cheap USB unit that I purchased, I can get flat calibrations. With the MobilePre, I'm not getting a flat calibration. And when I take measurements, whether using the calibration or not, I have huge spikes and peaks (which of course is possible from the room, but moving the mic doesn't help much), so I'm not trusting the results I see.

I'm running Windows XP on my laptop (older Dell unit).

Hmm, well, that would possibly rule out that the Vista driver from M-Audio is to blame.

I am pretty sure I had a very flat system cal on my old laptop which was a Toshiba Portege, with Xp Pro.

The thing is, I am never using TrueRTA's built-in generator, as I always use a pink-noise track on a CD (to also take into account the source units performance). So line-out isn't an issue for me at all really. But the line-in is, specifically the XLR Phantom powered (mic) input. I also use a Behringer ECM8000.

But I have no clue how linear the line-in is on the Mobile-Pre. When I do system cal on the stationary PC, its almost ruler flat to begin with, but as soon as I connect the darn thing to my Laptop, it looks like the Himalayas... :mad:

/Jonas

carbuff

11-27-07, 02:33 PM

But I have no clue how linear the line-in is on the Mobile-Pre. When I do system cal on the stationary PC, its almost ruler flat to begin with, but as soon as I connect the darn thing to my Laptop, it looks like the Himalayas... :mad:
/Jonas

I wonder if the problem is the quality of the power that is provided over the 2 different machines' USB ports?

I will try to plug my MobilePre into my desktop and see how it calibrates. I haven't tried that before.

Also, again, does calibrating the line-out to line-in make sense if you are in-fact using the Microphone input? What are you calibrating in that case?

krabapple

11-27-07, 03:52 PM

TrueRTA vs RoomEQ wizard -- any reason other than cost to go with one vs the other?

krasmuzik

11-27-07, 04:05 PM

I am not commenting on TrueRTA bugs - been a while since I used it - but I thought it was one of the better RTA's with a goal of measurement and generation precision.

But I think you have a fundamental misunderstanding about acoustic measures.

Are you expecting SPL measures to be spectral density - in which case the frequency resolution does not matter and you would get the same results?

A partial octave measure is something different, it is indeed a lesser SPL if you measure a finer octave fraction of the same source. This is simply because a larger fraction has more frequencies in it. Imagine that you have an orchestra of tuning forks each playing only one frequency. If they all play their frequency together - don't you think it would be louder than if only one frequency was played? Look more closely at the spectrum of a sine wave - it still contains energy at other frequencies! One would have to compute the RTA SPL values from the underlying FFT data to figure out if those increasing numbers are correct or not - but I would expect them to increase as you included more frequencies by increasing the bandwidth of the measure. Even if you had a highly accurate sign wave generator making an electronic measure with a very quiet noise floor - it is a fundamental to windowed DSP that you cannot measure a pure sign wave - to do so would require an infinite measure. You are also measuring the spectrum of the window you used to take a finite measure - and windows vary in terms of frequency spreading and noise floors. This is even more true with real instruments in real rooms - both of which have modal resonances and noise floors - it is impossible to play pure sinewaves even with tuning forks because the pure signal gets corrupted by the room.

This is a feature of acoustics and DSP - it is the way the physics and engineering work - it is not a bug to be fixed! TrueRTA may have real bugs - but that ain't one of them! As a professional I would be PO if the SPL did not change when I vary the octave fraction - a good sign there is a bug!

Anyways if you are needing a tool for professional work - shouldn't you pay for one that has a professional price so you can demand fixes and enhancements on your schedule? Good as TrueRTA may be - you can only expect so much for the Benjamin it cost....

I have found a critical data error bug in the Level 4 TrueRTA v3.3.3 RTA Octave Resolution display.

The on-screen and exported data points are invalid for all resolutions lower than 1/24 octave.

The user takes a measurement which is present in the Workbench.
When the user selects different RTA Resolution, i.e. 1/3 Octave, 1/6 Octave, the data values change.

The measurement has not changed. TrueRTA is changing the data point SPL values as it changes octave resolution.

This is dead wrong.

The bug is demonstrated by using 80 Hz as the sample frequency because 80 Hz is present in all octave resolutions except for 1 Octave.

In this example, a 100 Hz sine wave measurement was taken at 1/24 octave resolution.
Below are the results at 80 Hz.

1/24 Octave: 35.22 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-24_Resolution.jpg)
1/12 Octave: 38.11 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-12_Resolution.jpg)
1/06 Octave: 40.66 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-06_Resolution.jpg)
1/03 Octave: 43.95 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-03_Resolution.jpg)
1/01 Octave: 50.47 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-01_Resolution.jpg)

Exporting the Workbench verifies the onscreen dB values match the text file data.
The 1-octave resolution does not export 80 Hz, so only the screen point was used.

Every SPL data point on both on-screen and exported values are corrupt at all resolutions lower than 1/24.

jonash72

11-27-07, 04:41 PM

I wonder if the problem is the quality of the power that is provided over the 2 different machines' USB ports?

I will try to plug my MobilePre into my desktop and see how it calibrates. I haven't tried that before.

Also, again, does calibrating the line-out to line-in make sense if you are in-fact using the Microphone input? What are you calibrating in that case?

Well, I guess you are right, I mean I would actually like to be able to calibrate only the input, but, I dont think there is a way?!

Actually, when I think about it....could it get WORSE when I do a system cal the way it is described? I mean, let's assume that the output is real nasty, but the input is just fine. So now I get a calibration that will acount for a nasty output, of which i use none. But my measured response will still take into account a nasty output, even if there isn't one... :eek:

/Jonas

carbuff

11-27-07, 09:48 PM

Well, I guess you are right, I mean I would actually like to be able to calibrate only the input, but, I dont think there is a way?!

Actually, when I think about it....could it get WORSE when I do a system cal the way it is described? I mean, let's assume that the output is real nasty, but the input is just fine. So now I get a calibration that will acount for a nasty output, of which i use none. But my measured response will still take into account a nasty output, even if there isn't one... :eek:

/Jonas

That was the rationale that I came to when I decided to try and include my preamp in the calibration loop.

Digital out from PC -> PreAmp Digital In -> PreAmp Analog Line Out -> Analog Line In on PC Soundcard

That seems like the right way to do the calibration to me. But, in the MobilePre, that doesn't include the Mic In circuit, so I'm unsure whether the calibration is doing me any good...

I need to either drag my desktop into my den or move my preamp into my office to connect my MobilePre to the desktop and see if the calibration works any better...

jonash72

11-28-07, 02:08 AM

That was the rationale that I came to when I decided to try and include my preamp in the calibration loop.

Digital out from PC -> PreAmp Digital In -> PreAmp Analog Line Out -> Analog Line In on PC Soundcard

That seems like the right way to do the calibration to me. But, in the MobilePre, that doesn't include the Mic In circuit, so I'm unsure whether the calibration is doing me any good...

I need to either drag my desktop into my den or move my preamp into my office to connect my MobilePre to the desktop and see if the calibration works any better...

I think it may well have something to do with the USB bus power, because when I tried to calibrate without the AC adapter plugged into the wall (we have 220V/50Hz in Sweden) it looked even worse.

I would personally skip the calibration if it didnt look as bad as it does from the beginning.

On my stationary PC, the response through the soundcard is very flat to start with, probbaly within 1dB across the range. With the Laptop, it's not within 10dB.....

/Jonas

bgavin

11-28-07, 10:51 AM

http://www.bgavinsound.com/reference/music/test%20results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/small_composite.jpg

This is the octave resolution bug in visual form. I loaded a project into the Workbench and took two screen shots: one at 1/24 and the other at 1/3 octave. The data is the same project in both cases.

One is right, one is wrong. Which one?

Let's just refund your purchase and be done with this. How would you like to receive the refund? We can credit your card or send you a check. If you want a credit to your card then please provide a current expiration date for the original card. Please let me know your preference. Life is too short for this sort of nonsense.

John

The author is now pressing me to take a refund. I have declined the refund.

First, a refund gets him off the hook for fixing the bugs. Next and more subtle, it removes my right to continue reporting bugs in TrueRTA because I would no longer be a licensed user.

I replied that I do not want a refund, and that I will be entirely happy when the bugs are fixed. I will continue to report new bugs as I discover them. I have found another bug but not yet reported it. It is a very minor one with the file handling routines for project files. I will post it here when time permits.

It is obvious now the author's ego will not allow him to resolve my complaints. Therefore, the only way to get the bugs fixed will be for other users to test their systems and make bug reports. I am assembling a PDF that details all the bugs and how to test for them. If sufficient owners report these problems, the author will have to investigate and correct them.

All of the above is such a shame... TrueRTA is just exactly what I need once the bugs are fixed.

My test bench is a Dell Inspiron laptop running XP Pro. If you have Vista, all bets are off. IMO, wipe it clean and install XP (I own a computer firm). My USB interface is the Edirol UA-25 which provides phantom power to my Superlux mic, which uses the same capsule and calibration file as the Behringer mic.

This interface produces no more than 0.25v maximum output, so it won't drive a power amp to full power without an intermediate line amplifier. I use a Rane for this. I notice no improvement or degradation when using either a powered USB hub or an external +48v phantom supply. The Edirol works fine.

I use the TRTA signal generator because it allows for very fine control over the output voltage. This is far more sensitive than adjusting knobs. I do all my 8-ohm speaker measurements at 2.83 volts, and the generator dB setting allows me to dial this in exactly on my DVOM.

It is very important to follow ALL the calibration steps outlined here. TrueRTA is quite sensitive to mis-calibration. I suspect the data porting bug detailed above is somehow tied into the calibration file. The response of PC grade sound cards and onboard circuits requires TRTA calibration.

I have access to a Mobile-Pre device, but have not tested it. The Edirol box is smaller and does exactly what I require. If anybody needs assistance, please ask. I have been working TRTA a lot, and will offer whatever assistance is within my range of knowledge.

krabapple

11-28-07, 11:03 AM

one of the bugs you reported is not a bug, for reasons krazmusic explained. And from John's email it appears there has been some friction between the two of you in the emails you haven't shown.

John L. Murphy

11-28-07, 01:22 PM

Hello TrueRTA users!

Bruce is reporting measurement results that he thinks are the result of "bugs" in TrueRTA. I will address his complaints one at a time. I take all bug reports seriously as they help to improve the product.

I am a 33+ years professional programmer, and the corollary to this is “a feature is a bug with useful side effects.” This is the sort of denial one expects from Microsoft. It does nothing to correct the problem, so let's please stay focused on the bug.

Here’s the first problem restated:
1) TRTA geneartes a 100 Hz sine wave
2) Separate SPL meter reads 105 SPL
3) TRTA on-screen meter reads 106 SPL
4) TRTA on-screen data point reads 105 SPL
5) Export to TXT shows 100 Hz at 105 SPL

This is a point measurement, not broad band. The sine wave is 40dB higher than background. If TRTA is accumulating across the entire spectrum, it is still hearing 100 Hz at 40dB higher intensity than background.

I always calibrate TRTA to the SPL meter.
Do I calibrate TRTA to the Screen data point, or Screen Meter value?
Question: one is wrong, one is correct. Which one?

What Bruce is reporting here as a "bug" is actually normal behavior for any spectrum analyzer. Let me explain...again, and in more detail this time.

There are two distinct measurements being made by TrueRTA. There is a Narrowband measurement and a Broadband measurement. It is normal for them to be different. Sometimes the difference is small and sometimes it is large depending on the signal being measured.

The Broadband measurement is the reading from the TrueRTA SPL meter. This meters all the audio signals from 20 Hz to 20 kHz. The external SPL meter is also making a broadband measurement.

The Narrowband measurement is the reading taken from the individual RTA bar at 100 Hz. This reading only represents the energy within this narrow 1/24th octave wide band of frequencies.

Even though the narrow band at 100 Hz contains most of the measured energy, opening the bandwidth of the measurement to the full audio spectrum will add a slight bit more energy from all the additional frequency bands resulting in a higher SPL reading. This additional energy that is included in the broadband measurement is the difference between the readings of 105 vs. 106 dB SPL. This difference is perfectly normal and fully expected by those experienced with such measurements.

Note: When you perform TrueRTA's SPL calibration TrueRTA's SPL reading will instantly be adjusted to match the SPL of your calibration source. Most often this is a mic calibrator placed over the mic to be calibrated but you can also calibrate from another SPL meter. Just be sure to use an "unweighted" setting on your external meter when using it for calibration.

For those who want a little more depth here is a simple mathematical example showing how the two measurements are different:

Let's say we have one frequency "bin" with a signal level of 1.0 V. Define this level as 0 dB. Adjacent this bin are five bins on either side with "noise" at a signal level of .1 V (-20 dB).

The Narrowband measurement in this case would be the signal level of the single central band or simply 1.0 V or 0 dB. Let's name the Narrowband signal level "N".

N = 1.0 Volts = 0 dB

The Broadband measurement would consist of the combination of all the frequency bins. Let's name the Broadband measurement "B" and calculate it's value.

B = Sqrt(L1*L1 + L2*L2 + L3*L3 + L4*L4 + L5*L5 +L6*L6 +L7*L7 +L8*L8 + L9*L9 +L10*L10 + L11*L11 )

B = Sqrt( 0.1*0.1 + 0.1*0.1 +... + 1.0 +...+ 0.1*0.1 +0.1*0.1)

Where L1, L2 etc. are the signal levels at the individual frequency bins.

B = Sqrt(.01 + .01 + .01 + .01 + .01 + 1.0 + .01 + .01 + .01 + .01 + .01)

(note the five .01 signals on either side of the central 1.0 signal)

B = Sqrt( .05 + 1.0 + .05 )

B = Sqrt( 1.10)

B = 1.0499...

in dB

B = 20* Log (1.0499)

B = 0.414 dB

So in this simplified exmple we see a 0.414 dB rise in signal level for the wideband measurement versus the narrowband, single bin, measurement. The additional frequency bins of a broadband measurement will always increase the signal level.

You could also do a benchtop experiment with a variable width filter that would make the effect of bandwidth on signal level quite clear. Imagine this, you feed a pink noise source through a variable bandwidth filter and play the output signal over your speakers. Turn the volume up to say 90 dB SPL with the full bandwidth pink noise. Next start sweeping the filter (perhaps a crossover) upward from 20 Hz so that you start chopping off the low frequencies. The apparent sound level would decrease as would the reading of an external SPL meter. Narrowing the bandwith has lowered the signal level.

I hope from this it is clear that a single frequency measurement on the RTA will always be somewhat lower than the broadband SPL measurement seen at the SPL meter at the far left. Only in the ideal case where the noise in the adjacent bins was absolutely zero would the two measurements be the same.

Regards,

John

John L. Murphy

11-28-07, 02:44 PM

Hello TrueRTA users!

Bruce reports measurement results that he feels are the result of "bugs" in TrueRTA. I will address his complaints one at a time. I take all bug reports seriously as they help to improve the product.

I am a 33+ years professional programmer, and the corollary to this is “a feature is a bug with useful side effects.” This is the sort of denial one expects from Microsoft. It does nothing to correct the problem, so let's please stay focused on the bug.

Here’s the first problem restated:
1) TRTA geneartes a 100 Hz sine wave
2) Separate SPL meter reads 105 SPL
3) TRTA on-screen meter reads 106 SPL
4) TRTA on-screen data point reads 105 SPL
5) Export to TXT shows 100 Hz at 105 SPL

This is a point measurement, not broad band. The sine wave is 40dB higher than background. If TRTA is accumulating across the entire spectrum, it is still hearing 100 Hz at 40dB higher intensity than background.

I always calibrate TRTA to the SPL meter.
Do I calibrate TRTA to the Screen data point, or Screen Meter value?
Question: one is wrong, one is correct. Which one?

This is perfectly normal behavior for any spectrum analyzer. Let me try to explain... in more detail this time.

There are two distinct measurements being made by TrueRTA. There is a Narrowband measurement and a Broadband measurement. It is normal for them to be different. Sometimes the difference is small and sometimes it is large depending on the nature of the signal being measured.

The Broadband measurement is the reading from the TrueRTA SPL meter. This meters all the audio signals from 20 Hz to 20 kHz. The external SPL meter is also making a broadband measurement.

The Narrowband measurement is the reading taken from the individual RTA bar at 100 Hz. This reading only represents the energy within this narrow 1/24th octave wide band of frequencies.

Even though the narrow band at 100 Hz contains most of the measured energy, opening the bandwidth of the measurement to the full audio spectrum will add a slight bit more energy from all the additional frequency bands resulting in a higher SPL reading. This additional energy that is included in the broadband measurement is the difference between the readings of 105 vs. 106 dB SPL. This difference is perfectly normal and fully expected by those experienced with such measurements.

Note: When you perform TrueRTA's SPL calibration TrueRTA's SPL reading will instantly be adjusted to match the SPL of your calibration source. Most often this is a mic calibrator placed over the mic to be calibrated but you can also calibrate from another SPL meter. Just be sure to use an "unweighted" setting on your external meter when using it for calibration.

For those who want a little more depth here is a simple mathematical example showing how the two measurements are different:

Let's say we have one frequency "bin" with a signal level of 1.0 V. Define this level as 0 dB. Adjacent this bin are five bins on either side with "noise" at a signal level of .1 V (-20 dB).

The Narrowband measurement in this case would be the signal level of the single central band or simply 1.0 V or 0 dB. Let's name the Narrowband signal level "N".

N = 1.0 Volts = 0 dB

The Broadband measurement would consist of the combination of all the frequency bins. Let's name the Broadband measurement "B" and calculate it's value.

B = Sqrt(L1*L1 + L2*L2 + L3*L3 + L4*L4 + L5*L5 +L6*L6 +L7*L7 +L8*L8 + L9*L9 +L10*L10 + L11*L11 )

B = Sqrt( 0.1*0.1 + 0.1*0.1 +... + 1.0 +...+ 0.1*0.1 +0.1*0.1)

Where L1, L2 etc. are the signal levels at the individual frequency bins.

B = Sqrt(.01 + .01 + .01 + .01 + .01 + 1.0 + .01 + .01 + .01 + .01 + .01)

(note the five .01 signals on either side of the central 1.0 signal)

B = Sqrt( .05 + 1.0 + .05 )

B = Sqrt( 1.10)

B = 1.0499...

in dB

B = 20* Log (1.0499)

B = 0.414 dB

So in this simplified exmple we see a 0.414 dB rise in signal level for the wideband measurement versus the narrowband, single bin, measurement. The additional frequency bins of a broadband measurement will always increase the signal level.

You could also do a benchtop experiment with a variable width filter that would make the effect of bandwidth on signal level quite clear. Imagine this, you feed a pink noise source through a variable bandwidth filter and play the output signal over your speakers. Turn the volume up to say 90 dB SPL with the full bandwidth pink noise. Next start sweeping the filter (perhaps a crossover) upward from 20 Hz so that you start chopping off the low frequencies. The apparent sound level would decrease as would the reading of an external SPL meter. Narrowing the bandwith has lowered the signal level.

I hope from this it is clear that a single frequency measurement on the RTA will always be somewhat lower than the broadband SPL measurement seen at the SPL meter at the far left. Only in the ideal case where the noise in the adjacent bins was absolutely zero would the two measurements be the same.

Regards,

John

bgavin

11-28-07, 03:58 PM

I will endure no more of your unpleasantness.

Your license to use TrueRTA is hereby officially revoked. The full purchase price of $99.95 has been refunded to your VISA card ending with the digits 0190. You are directed to uninstall TrueRTA from all computers on which you have it is installed.

John
This does nothing to address the 10dB difference between 1/3 and 1/24 octave resolution.

This does nothing to address the data portability bug, where the .RTA data points are altogether different when moved to a different machine.

Yes indeed there is friction. I sent a bug report and asked for the favor of a reply. After a week, I got none, so I called. Sharon told me the bug report was still in the inbox, unread. It was forwarded directly to John.

John claims my mail server rejected many of his attempts. Probably, if his provider is on the black hole list. But.. I provided two email addresses for contact, and when contact was made, it was hostile.

As a customer, I don't like being blown off. I have found serious and repeatable data errors in TrueRTA and have been repeatedly blown off. John has revoked my user license which allows him to glibly ignore these bugs, and simultaneously prevents me from reporting new ones.

All I want is the bugs fixed. Not a bunch of math and hogwash.

John L. Murphy

11-28-07, 03:58 PM

Here is Bruce's next bug report along with my explanation of why the observed behavior is not really a bug but rather normal behavior for a variable resolution RTA.

I have found a critical data error bug in the Level 4 TrueRTA v3.3.3 RTA Octave Resolution display.

The on-screen and exported data points are invalid for all resolutions lower than 1/24 octave.

The user takes a measurement which is present in the Workbench.
When the user selects different RTA Resolution, i.e. 1/3 Octave, 1/6 Octave, the data values change.

The measurement has not changed. TrueRTA is changing the data point SPL values as it changes octave resolution.

This is dead wrong.

The bug is demonstrated by using 80 Hz as the sample frequency because 80 Hz is present in all octave resolutions except for 1 Octave.

In this example, a 100 Hz sine wave measurement was taken at 1/24 octave resolution.
Below are the results at 80 Hz.

1/24 Octave: 35.22 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-24_Resolution.jpg)
1/12 Octave: 38.11 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-12_Resolution.jpg)
1/06 Octave: 40.66 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-06_Resolution.jpg)
1/03 Octave: 43.95 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-03_Resolution.jpg)
1/01 Octave: 50.47 dB (http://www.bgavinsound.com/reference/Music/Test%20Results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/80Hz_1-01_Resolution.jpg)

Exporting the Workbench verifies the onscreen dB values match the text file data.
The 1-octave resolution does not export 80 Hz, so only the screen point was used.

Every SPL data point on both on-screen and exported values are corrupt at all resolutions lower than 1/24.

TrueRTA is giving correct results. As the resolution is increased from 1 octave to 1/24th octave each band is measuring less and less of the everpresent broadband background noise and the level of each bar drops accordingly. The overall effect is that at higher resolutions you can see increasing detail at lower and lower levels. For example, each bar of the 1 octave display bar contains a higher level of energy than an individual bar of the 1/24th octave display. This is reflected in the higher level of the noise floor in the 1 octave measurements.

Bruce is measuring a 100 Hz signal and is surprised that the level of the 80 Hz band goes down as the resolution increases. But this is actually perfectly normal and expected bahavior. The higher resolution measurement reveals a lower noise floor. TrueRTA is reporting the levels of both the 100 Hz signal and the 80 Hz signal correctly.

In the following sequence you can see how a pink noise measurement drops in level as the resolution is increased. Meanwhile, the broadband signal level would be constant and independent of this change in resolution of the analyzer.

http://www.trueaudio.com/images/rta_scrn31.gif
http://www.trueaudio.com/images/rta_scrn32.gif
http://www.trueaudio.com/images/rta_scrn33.gif

This is perfectly normal behavior for any variable resolution spectrum analyzer. TrueRTA is performing just as it should. Any other behavior would be incorrect.

In summary, the shift in the noise floor to lower and lower levels as the resolution of the analyzer is increased is proper behavior for any spectrum analyzer.

Regards,

John

bgavin

11-28-07, 04:20 PM

http://www.bgavinsound.com/reference/music/test%20results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/small_composite.jpg

The above is two interpretations of a single trace.
The RTA was calibrated to an external SPL meter reading 92 SPL for a 100 Hz sine wave.

The 1/24 octave sweep correlates with the SPL meter at 100 Hz.
Changing resolution to 1/3 octave boosts the 100 Hz SPL reading on screen to 102 SPL.

If I used the 1/3 octave trace, it would be in error by +10dB.

krasmuzik

11-28-07, 04:29 PM

Good luck finding a spectrum analyzer that defies the laws of physics and DSP that you can use in your professional work.....

jonash72

11-28-07, 05:37 PM

Hmm, I am not sure if I remember the older versions of TrueRTA doing that, I have verified in my own version 3.3.3 that it does shift the amplitudes when switching from say 1/3rd to 1/24.

HOWEVER, I beleive this is the way it is supposed to be. Because when doing a 1/3rd octave analysis, you get 8times the number of bins in your total SPL number vs the 1/24th resolution. So, each bin in the 1/3rd octave analysis will have ALOT more energy recorded and stored, and eventually displayed.

I guess the real question may be:

How do we use TrueRTA to get the real SPL numbers? Or rather, how is this calibration procedure performed.

Personally, I dont give a rats behind about the SPL numbers, as I am only looking at the response curves, but I do see why it would be of some significance to some.

I _think_ there is probably an easy workaround for this, as it should be a fairly simple mathematical excercise to get the correct SPL numbers for any resolution.

So, I am pretty sure that John will either tell us what our problem, or, he will put a new version to download for us all.

/Jonas

http://www.bgavinsound.com/reference/music/test%20results/TrueRTA%20Bugs/Octave%20Resolution%20Bug/small_composite.jpg

The above is two interpretations of a single trace.
The RTA was calibrated to an external SPL meter reading 92 SPL for a 100 Hz sine wave.

The 1/24 octave sweep correlates with the SPL meter at 100 Hz.
Changing resolution to 1/3 octave boosts the 100 Hz SPL reading on screen to 102 SPL.

If I used the 1/3 octave trace, it would be in error by +10dB.

bgavin

11-28-07, 06:08 PM

HOWEVER, I beleive this is the way it is supposed to be. Because when doing a 1/3rd octave analysis, you get 8times the number of bins in your total SPL number vs the 1/24th resolution. So, each bin in the 1/3rd octave analysis will have ALOT more energy recorded and stored, and eventually displayed.
Question for you: did the sound get 10dB louder by changing chart resolution?

The end result of RTA is not how many bins are filled, nor how many angels dance on the head of a pin. The result is supposed to show you the SPL of the signal level. 1/24 is accurate, 1/3 is inflated +10dB.

krasmuzik

11-28-07, 10:53 PM

Can you tell me what 8x more is in dB?

The bandwidth is increased 8x - thus there is 8x more signal than there was before. The only way there could be the same amount of signal would be to reduce the per frequency amount by 8x. This is a real time signal analyzer - you increased the bandwidth of the filter and have 8x more data - it is not simply a matter of changing a chart resolution. It has nothing to do with what your SPL meter said - which is not using bandwidth filters to look at the signal as individual pieces. The only reading that should correlate with the SPL meter in your hand - is the SPL meter in the software. This chart is NOT an SPL meter it is an RTA curve in units of SPL. What if that was volts per frequency - would you expect a voltmeter to be the same reading? How is it that you decided that 92SPL at 100Hz was the SPL meter reading - why can't it be that the answer is the 86SPL at 50Hz? Why not correlate the reading at 80SPL at 400Hz? How much frequency range is there in the 24th octave centered on 125Hz vs 3rd octave?

How much more dB do you think there should be? You said you are a professional using this signal analyzer - what is the answer?

jamin

11-29-07, 02:58 AM

For those that realize the earth is not flat just move along --there is nothing to see here.

Otherwise: Many well intentioned individuals have tried to explain how this measurement works. I will now use the method of cows.

There are 24 cows in each octave. With 10 octaves across the audio band, that means there are a total of 240 cows.

First I will make a plot of cows using a 1/3 octave resolution. Lo and behold there are 8 cows in each 1/3 octave.

Next I will make a plot of how many cows there are in each 1/24 octave. Well my goodness, there is only one cow in each 1/24 octave.

Is my second plot right or wrong compared to my first plot? If I add up all of the cows in each instance did the total number of cows change?

Of course the total number of cows did not change. Each measure of cows in a fraction of an octave was also correct.

What exactly did you want to measure?

jonash72

11-29-07, 03:21 AM

Question for you: did the sound get 10dB louder by changing chart resolution?

The end result of RTA is not how many bins are filled, nor how many angels dance on the head of a pin. The result is supposed to show you the SPL of the signal level. 1/24 is accurate, 1/3 is inflated +10dB.

Yes, the graph "jumps up" ~10dB when I switch between resolutions, but I understand why it does so, as you have so much mure total energy in each bin for a 1/3rd octave analysis vs a 1/24th.

However, I do agree it would be nice to have the option in the Software for an automatic "adjustment" of the SPL axis when switching resolutions. A simple check-box in the Preferences/Options dialog box or some such.

/Jonas

jamin

11-29-07, 03:43 AM

If you are going to invalidate the measurement, what erroneous levels would you choose for which particular resolutions. Of course if would not be an RTA at that point.

That reminds me, I have both a laser interferometer and a mass spectrometer and neither one of those silly things reads the way I want them to. Gotta remember to call the manufacturers and ask them to trash those measurement instruments for me.

Jeez, don't you just hate those standards organizatons? Everyone measuring the same things the same ways all over the planet. How boring :)

bgavin

11-29-07, 10:59 AM

bgavin

11-29-07, 11:03 AM

What exactly did you want to measure?
I wanted to measure the height of the cows.

One cow, or 10 ten cows, the height does not change. I want to know the height of the cow standing at a particular point. I don't care about the weight of the other cows around it, nor how many cows there are.

If I have a cow standing at the 100 Hz point and change octave resolution, the cow does not get taller.

protos

11-29-07, 11:52 AM

jamin

11-29-07, 11:54 AM

The cows represent the energy in an octave.
The RTA functions as it should and as they all do.

krabapple

11-29-07, 01:04 PM

John L. Murphy

11-29-07, 02:43 PM

Well, that was certainly a helpful contribution.

What I cannot understand is, why the graph jumps +10 when the actual levels have not changed.

What I wanted to see was the data points interpreted on a 1/3 octave basis. Since that doesn't happen in TrueRTA, that make TrueRTA useless for my needs. I cannot measure a speaker cabinet and publish graphs that are inflated +10dB. Bass players certainly won't understand bins, etc.

It is actually very simple. The signal levels in each bin DO change precisely as indicated by TrueRTA. Narrower filters measure a lower signal level. Maybe another example will help make it clear why the shift is both necessary and correct.

The sequence below shows what happens when you change resolutions after measuring a sine wave at 0 dBu. Notice that the peak at 500 Hz remains at the same level as we change resolutions. But the broadband noise floor decreases as the resolution is increased...as it must. Each 1/24 octave bin is measuring only a fraction of the signal measured by the 1 octave wide frequency bins. But the bin at 500 Hz measures a constant signal level as that bin is made narrower. This is because the 500 Hz bin is being stimulated primarily by a single frequency. So the 500 Hz tone remains constant around 0 dBu even as the resolution is changed. The remaining bins are measuring mostly white noise and as such they fall in level as the bin is made more narrow.

http://www.trueaudio.com/images/rta_scrn34.gif
http://www.trueaudio.com/images/rta_scrn35.gif
http://www.trueaudio.com/images/rta_scrn36.gif

For those engineers seasoned in such measurements this is a normal and expected behavour. But occasionally someone less experienced in electronic measurements will question why the noise floor shifts.

Regards,

John

John L. Murphy

11-29-07, 02:49 PM

Hi,
I am testing the free version but first of all it is only outputting sinewave and pink noise.The sinewave level is frequency dependent!Although clean it may be eg 2000mv at 400hz and then at 800hz it drops to something like 1000mv then it goes up again at 1khz to 1500mv then drops again and so on , at freq above 5khz i cannot even read the signal because it drops too low.On square wave or triangle wave I see a small sine wave residual and occasinally some kind of impulse on the screen.Is this a bug because it cannot be the way it functions?

Make sure you have any sound card special effects or "monitoring" turned off as this can lead to the kind of response you describe. Also try reducing your generator level. You may be overdriving the sound card output which can lead to erratic results.

Regards,

John

John L. Murphy

11-29-07, 02:57 PM

bgavin

11-29-07, 04:05 PM

Notice that the peak at 500 Hz remains at the same level as we change resolutions. But the broadband noise floor decreases as the resolution is increased...as it must.

For those engineers seasoned in such measurements this is a normal and expected behavour. But occasionally someone less experienced in electronic measurements will question why the noise floor shifts.

John
I don't have a problem with the noise floor. I have a problem with the peak shifting +10dB. My sources are in the 100 to 136 dB range, so the noise floor is inconsequential to the intensity of the sine wave.

As I understand a swept sine, each point is driven at full voltage. This is an automated method of taking discreet measurements at single frequencies. When I sample at point at 1/24 it correlates with the external meter. The same point at 1/3 is higher by 10dB than the meter.

Your example above shows the 500 Hz peak does not change amplitude with resolution. This is exactly what I wanted from Level 4, but did not get. I notice you are using dBu, and I was using SPL.

krasmuzik

11-29-07, 04:17 PM

bgavin

Please answer why you chose to sample the point that correlated your SPL meter - rather than another frequency on the curve which does not.....

bgavin

11-29-07, 04:31 PM

The cows represent the energy in an octave.
The RTA functions as it should and as they all do.

Perhaps.

My concern is not with dogma, but with finding an understanding why a peak point value changes +10 dB between resolutions.

I understand the QuickSweep is a series of 1/24 bins, individually sampled. Therefore, the amount of energy in the octave is irrelevant. Only the energy in each bin is relevant. This displays correctly at 1/24.

Changing to 1/3 evidently sums all the bins, instead of charting between points relevant to 1/3 resolution. This summing boosts the graph by +10dB, yet the measured bin data does not change.

If the chart were drawn between points at 1/3 octave, i.e. 80, 100, 125, 160 Hz using the measured bin data, this would produce a chart at the sample amplitude, but at 1/3 resolution.

protos

11-30-07, 09:26 AM

Make sure you have any sound card special effects or "monitoring" turned off as this can lead to the kind of response you describe. Also try reducing your generator level. You may be overdriving the sound card output which can lead to erratic results.

Regards,

John

Thanks John but I have followed the recmmendations about setting up the audio card i.e.no effects etc.I have adjusted windows and the outputs mixers of the card (Sounblaster live) which are VERY sensitive (just a couple of percent and the output jumps to double on the mv range!) and as I said the sinewave looks clean i.e. no clipping.I have played with the generator level but it does not affect the results that much unless I overdrive it of course.Also the fact that I cannot see any form of square wave is strange.I am thinking of buying a full version but only if I am sure I can sort this out.

protos

11-30-07, 10:00 AM

I am playing around with various settings but no go.First of all if I am seeing a nice sinewave it means the input output settings are correct.I can see a triangle (although it is not really sharp at the point)and pink noise and saw waves but i cannot see a square wave even though the mv meter is registering something like 2000mv on this setting.The sine wave is good now up to like 3khz then drops to zero level.I have not set any equalizer or effects.On the square wave if I set the oscilloscope to to very gross ms divisions i can see something like an impulse response i.e. a thick line with intermittent spikes but no square waves or similar on any setting.I guess the frequency aberration i.e. nothing above 3khz is affecting the square wave production since even low hz square waves need higher harmonics , right?

protos

11-30-07, 10:32 AM

The other weird thing on the sinewave is that as I increase the gen level up to +10 dbu i get about 200mv approx. for every db increase then after +10dbu the level instead of increasing starts dropping even though there is no clipping evident.In fact at +20 dbu the level drops to almost zero.
Also if I go down to 100hz sinewave and change the output level by 1dbu ie from 18 dbu to 17 dbu the output level jumps from 2600mv down to 1600mv!

John L. Murphy

11-30-07, 11:20 AM

I don't have a problem with the noise floor. I have a problem with the peak shifting +10dB. My sources are in the 100 to 136 dB range, so the noise floor is inconsequential to the intensity of the sine wave.

As I understand a swept sine, each point is driven at full voltage. This is an automated method of taking discreet measurements at single frequencies. When I sample at point at 1/24 it correlates with the external meter. The same point at 1/3 is higher by 10dB than the meter.

Your example above shows the 500 Hz peak does not change amplitude with resolution. This is exactly what I wanted from Level 4, but did not get. I notice you are using dBu, and I was using SPL.

Let's go over it again. These measurements are not trivial and take a while to understand. This time I'll use the SPL mode to demonstrate that a measured peak does not change in level as you go from 1 to 1/3 to 1/24 octave resolution. The measurement depends strongly on the nature of the signal present in each frequency bin. A bin with a single strong frequency will remain constant in level but a bin with noise (many frequencies) will fall with increasing resolution as the filter is narrowed. Note that a bin with a mix of a small peak (say a distortion component) and noise will reveal the peak better as the bins narrow and the noise is reduced to reveal the peak. Here is a measurement of the speaker in my notebook PC along with lots of ambient noise to add character to the measurement.

http://www.trueaudio.com/images/rta_scrn37.gif
In the 1 octave resolution shot above we see the peak at 300 Hz only generally defined with a hint of a second peak at 60 Hz. The peak reads close to the broadband SPL level of 80 dB. The noise floor appears around 50 dB SPL when seen through 1 octave wide filters.

http://www.trueaudio.com/images/rta_scrn38.gif
The 1/6 octave resolution shot above reveals the presence of a 2nd harmonic distortion component at 600 Hz and perhaps a 4th harmonic at 1200 Hz. A broad peak is seen near 60 Hz. The 300 Hz peak is seen unchanged at 80 dB SPL but the 60 Hz peak has fallen in apparent level from about 57 dB in the 1 octave measurement to about 53 dB in the 1/6 octave measurement. The noise floor appears around 44 dB SPL when seen through 1/6 octave filters.

http://www.trueaudio.com/images/rta_scrn39.gif
Finally, in the 1/24 octave resolution shot above we see the 2nd and 4th harmonics sharply revealed. We also see that the 60 Hz peak is actually two separate peaks at 50 and 60 Hz. Note that the 300 Hz peak remains UNCHANGED at 80 dB SPL while the 2nd harmonic level also remains constant as the 4th drops slightly as noise is eliminated from its bin. The noise floor appears around 38 dB SPL when seen through 1/24 octave filters.

Most importantly, note that the peak amplitudes remains constant as the resolution is changed. The noise floor drops at higher resolution to reveal the smaller peaks. It is easier to see what is happening here than it is with a pink noise response so in a subsequent post I will show what happens with a pink noise response as resolution is changed. I'l also show how to shift a pink noise measurement to calibrate it up to a fixed pitch SPL measurement.

A Personal Note to TrueRTA Users:

Meanwhile, I am busily working on a maintenance release of TrueRTA to fix a verifiable bug affecting a major industrial user. When reliable users report bugs that I can reproduce I take them very seriously even if I can't fix them immediately. I'm not sure the minor "import bug" (discussed above) will be addressed in this release but I will be investigating it further.

You may have noticed that as a small software publisher I do all my own customer support. This takes a lot of time and sometimes my responses are delayed more than you (and I) would like. I really enjoy making powerful audio software available at a price the represenst a high value to users. But I am sometimes tempted to charge a separate fee for support! I would much rather spend my time expanding the software. That is why I am highly appreciative of the AVS Forum hosting this thread, and for you TrueRTA users supporting each other here as you do. This allows me to spend more time developing new software. I actually have in the works a powerful new impulse analyzer that will allow analysis of signal arrival times and reflections. But this sort of project requires focused concentration with lots of quiet time to work out all the details.

I want to offer a warm Thank You to all TrueRTA users for helping to make this product sucessful and supporting my small software business.

John

protos

11-30-07, 12:05 PM

Looking at the spectrum analyzer with pink noise it shows these anomalies.The response is flat to about 1khz witha peak at 2khz and then it drops all the way down.Is this a bug of the freeware or coud it be my soundcard?
I have tested the signal generator on speakers and it seems to have a response up to high frequencies ie 16khz but this is just personal acoustic impression without mic measurements.So the problem is in the input side probably.Either the input is being equalized in some way or what?
By the way how do you attach a screenshot?

bgavin

11-30-07, 12:32 PM

This time I'll use the SPL mode to demonstrate that a measured peak does not change in level as you go from 1 to 1/3 to 1/24 octave resolution.

John
I absolutely agree.

You continue to focus on the single peak, but that was not the bug report. I only see 0.3dB change in a single sine peak between 1/24 and full octave resolution. My bug report was concerned with swept sine traces, not single points.

In field use, the whole 1/3 vs. 1/24 issue is avoided by not using 1/3. The 1/24 sweep is accurate, and that did the job. If I wanted 1/3 charts, I can dump to TXT and extract the 1/3 octave data values for plotting.

What is more important to other TRTA owners, is fixing the .TXT import problem that you said can be improved.

The other important one is investigating why a .RTA on a laptop provides wildly different results when moved to a desktop machine. The laptop had the sound system calibration and the USB sound card interface. The desktop had no calibration file, and was not using a sound card. It was for charting purposes only, but the results were very different for the same .RTA file.

I may be the only one who had the data portability problem, but it showed on up three machines. All the machines without sound cards and calibration files were the same. The laptop with sound card and calibration file was different. Right or wrong, the data is not portable between my machines.

The refund from TrueRTA posted to my credit card, so I have removed TRTA and can do no further testing or reporting.

jonash72

12-01-07, 12:46 PM

I absolutely agree.

You continue to focus on the single peak, but that was not the bug report. I only see 0.3dB change in a single sine peak between 1/24 and full octave resolution. My bug report was concerned with swept sine traces, not single points.

In field use, the whole 1/3 vs. 1/24 issue is avoided by not using 1/3. The 1/24 sweep is accurate, and that did the job. If I wanted 1/3 charts, I can dump to TXT and extract the 1/3 octave data values for plotting.

What is more important to other TRTA owners, is fixing the .TXT import problem that you said can be improved.

The other important one is investigating why a .RTA on a laptop provides wildly different results when moved to a desktop machine. The laptop had the sound system calibration and the USB sound card interface. The desktop had no calibration file, and was not using a sound card. It was for charting purposes only, but the results were very different for the same .RTA file.

I may be the only one who had the data portability problem, but it showed on up three machines. All the machines without sound cards and calibration files were the same. The laptop with sound card and calibration file was different. Right or wrong, the data is not portable between my machines.

The refund from TrueRTA posted to my credit card, so I have removed TRTA and can do no further testing or reporting.

I bet that if you import the calibration files into your desktop PC, it will plot the exakt same graphs as your Laptop does...

/Jonas

jonash72

12-05-07, 02:12 AM

Just wanted to let you know that after having gone through hell to get XP installed on my Laptop (it is a HP/Compaq and I think they do something to the hardware to prevent us from installing anything else than what is pre-installed, in this case Vista) - I have been able to calibrate the soundcard for a straight and smooth response.

(XP is still not installed 100% correctly)

But it works good enough so to speak. I can use my Laptop with TrueRTA again!

/Jonas

protos

12-05-07, 08:09 AM

jonash72

12-05-07, 05:44 PM

Hey guys,
I would appreciate some feedback and help setting up my rta.Nobody seems to have a n answer.
I checked my set up according to rta pdf instructions and it seemed correct.I followed set up instructions for soundblaster boards.
After pulling my hair out with the results I started playing with the in out connection cable.You can imagine my surprise that I could still get adjustable sinewaves on the screen etc even with this disconnected completely.This is with wave/mp3 input.On the line in input with the cable in I only get noise on the screen that does not change no matter how I adjust various settings in the mixer or the rta itself.
So all my comments about roll off in high freq apply to measurements that were made using the wave/mp3 input but that seems to be connected internally in the soundcard.
Using the line in input I only get noise on the screen.
I would appreciate some advice.
Thanks.

Check your Machine Configuration / Hardware Config. Make sure nothing besides the Soundblaster is active.

Then, connecting a simple 1/4" line STEREO cable fron line out to line in, really should do it. Are you conneccting it to line in or mic in?

In TrueRTA, set the channels to L+R. See if that changes anything. I sometime get the same type of "noise" on the screen, thats when i realizre I have Left Ch activated and running the mic on right.....

Next is to make sure the levels for input (record) and output is set correctly.

/Jonas

/Jonas

protos

12-07-07, 10:16 AM

Thanks Jonas.
I tried changing the l/r settings but this does not change anything.The line in is correct because if I lower the mixer volume control the noise goes to zero so obviously it is receiving some kind of input.Very high noise judging by the scope.
Funny thing if I connect amp/speakers to the soundcard output then I get an adjustable tone right up to the high frequencies using the wave/mp3 control.It does not seem to roll off after 3khz.However I do hear a fast clicking sound on top of the tone which must be a digital problem.
Also strange is that while running the output to the speakers as I said I can see the rta sine waves on the scope when wave/mp3 input is on.Just that after 3khz I can see practically nothing on the scope although I can hear clearly up to 14khz on the speakers.

mrbombastic

12-19-07, 08:24 AM

Can somebody explain how to use TrueRTA to measure speaker impedance. Thanks

thazy2

12-19-07, 11:11 PM

but at least im trying : )

i have been researching RTA for several months, and even pruchased WinMLs2004 per board member recommendation. Sad to say, i cannot get it to work. But now i would like to try TrueRTA. Will this software do thiS?

btw, isnt this suppose to be a file that u download?

thank you........................Jason

thazy2

12-19-07, 11:11 PM

hmmmm

thazy2

12-19-07, 11:12 PM

sorry, need to show url

thazy2

12-19-07, 11:13 PM

https://www.diymobileaudio.com/forum/showthread.php?t=17

http://personal.inet.fi/private/ilkka/BehringerECM8000corrections.txt

bgavin

12-23-07, 07:31 PM

I bet that if you import the calibration files into your desktop PC, it will plot the exakt same graphs as your Laptop does...
/Jonas
John has fixed this bug and released it in the 3.3.4 version.

tfowler

01-18-08, 09:31 AM

jonash72

01-22-08, 08:09 AM

I'd like to ask the members of this group about their experience in using TrueRTA to actually measure the response of their loudspeakers in their room environment. What is a good figure-of-merit for in-room performance, over say the 40-10000 Hz range? I've been using 1/3 octave and getting about plus or minus 4 db, with average deviation about 1.16 db. Given the individual aspects of room acoustics, extremely flat response is probably unobtainable, but what would be good in-room performance? Also, what resolution is best for this measurement? Tone controls, level controls, crossovers, etc. only give a crude modification ability compared to 1/24 or even 1/6 octave resolution. 1 octave seems too coarse, which is why I settled on 1/3 octave, but I'd be interested in the opinions and experiences of others.

1/3rd octave is the one that is commonly used, so that is perfectly fine. of course, one can look at higher resolutions as well to closely examine certain areas, but if we talk about frequency response of a loudspeaker, it is almost always in reference to 1/3rd octave res.

And, +-4dB in a home environment is actually a very good result IMO. I often see +-10dB, especially in the 100Hz and down region.

/Jonas

tfowler

01-31-08, 10:34 AM

1/3rd octave is the one that is commonly used, so that is perfectly fine. of course, one can look at higher resolutions as well to closely examine certain areas, but if we talk about frequency response of a loudspeaker, it is almost always in reference to 1/3rd octave res.

And, +-4dB in a home environment is actually a very good result IMO. I often see +-10dB, especially in the 100Hz and down region.

/Jonas
To continue this discussion, I just got a Behringer ECM8000 and was doing further measurements. I notice that the response I get with a quick sweep differs significantly from pink noise in the sub-1000 Hz range, but especially in the sub-200 Hz range. I assume that this is due to the fact that the quick sweep is so quick that room resonances don't have time to build up. For a response curve, I'm averaging quick sweep and pink noise measurements, since music consists of quick transients (measured by the quick sweep) and sustained notes (measured by the pink noise). What is the experience of other members of this group? Do you have better ways to make overall in-room response measurements? I don't pretend to be any sort of expert. Thank you!

rumonkey2

03-02-08, 01:01 PM

Is the 1 octave/free version enough to get you "initiated" on using this?

And how about, while learning, just using my "auto-setup" mic from my HK AVR240?

If I find useful/spend time to learn, then I would purchase 1/3 Octave & a decent mic....

Thanks...

Silent_Sound

03-09-08, 09:14 PM

Which microphone do you have?

To your questions: You have to forget the internal soundcard of the laptop.

(1) In normal use (once all is calibrated) the proper setup is (a) mic into XLR input or into line-in (1/4") of FastTrack and (b) FastTrack into laptop via the USB port and (c) Fastrack headphone out or Fastrack stereo RCA output into receiver's line-in (for sending the pink noise, etc, signal to the speakers.).

(2) In calibration loop/setup (a) from headphone out or stereo RCA output of Fastrack into XLR input or line-in (1/4") for the FastTrack and (b) USB from the FastTrack into the laptop via the USB port.

I have the M-Audio Mobile Pre, and I'm trying to figure out how to set it up, so that I can get the solid line, like the beginning of the post states...
I have connected it both ways below...BTW this is for the Calibration (loop/setup)

(1)
From headphone output of M-Audio to stereo mic in of M-Audio (both 1/8") and USB out to laptop.

(2)
I have also tried stereo line out to mic line in and usb to computer....still to no change.

Can anyone give me some pointers? Is there something that has to be set up in True RTA?
I followed the directions it said to use for "Sound System Calibration"

Help would be greatly appreciated.
Thanks

segoshi

03-22-08, 11:33 AM

I got ECM8000/Rolls MP13 pre/Sound Blaster Live 24. Originally, I had a problem by connecting MP13 into the mic input of the internal sound card of my laptop (weird reading), so I got SB Live 24 and connected it to the line-in. Now, TrueRTA sound card calibration did seemed to work fine, but it doesn't respond to the mic at all! SB Live seems to be working fine (I checked all other functions and performed the self test). When I went back to the original internal sound card by changing the default setting of the sound device, it does respond to the mic feed although the reading is screwed up. What am I doing wrong?

Segoshi

jonash72

03-26-08, 10:41 AM

I have the M-Audio Mobile Pre, and I'm trying to figure out how to set it up, so that I can get the solid line, like the beginning of the post states...
I have connected it both ways below...BTW this is for the Calibration (loop/setup)

(1)
From headphone output of M-Audio to stereo mic in of M-Audio (both 1/8") and USB out to laptop.

(2)
I have also tried stereo line out to mic line in and usb to computer....still to no change.

Can anyone give me some pointers? Is there something that has to be set up in True RTA?
I followed the directions it said to use for "Sound System Calibration"

Help would be greatly appreciated.
Thanks

If you are runing Windows Vista, you wont be able to do it. The drivers from M-Audio doesnt work with Vista, or if its TrueRTA or a combo.

I had bought a new Laptop with Vista pre-installed, and I had to use XP as OS instead. Then it worked right away...

/Jonas

karos

03-31-08, 04:23 PM

i decided to go with the m-audio fast track pro. i will be using it for other things as well, but for this project (analyzing a car or a room audio system) it will work well with a behringer mic. I read the bit about calibrating a pc - TRUE RTA for dummies (http://www.avsforum.com/avs-vb/showt...=572477&page=6) but am a little confused because of the multitude of in/outputs on the fast track pro. there are 2 balanced inputs for 2 microphones. these inputs are actually combo jacks that accomodate either an xlr(for a mic) or a TS(for a guitar or keyboard)

i assume to calibrate this device, i would need to go from the balanced trs outputs to the balanced mic inputs, yes? this would require male TRS-> male XLR

Or should i go this way: rca output -> TS male mic connection?

or should i go from headphone jack->splitter-> 2 TS male mic connections

what about the voltages-if i use the headphone vs balanced out vs unbalanced out and pipe that into the microphone input---wont i blow the mic input? after all the microphone usually does not supply voltage and phantom power is coming out of the microphone jack. In setting up a calibration loop, we are piping voltage into the microphone circuit.

karos

04-02-08, 12:44 PM

can anyone shed light on this? or at least a link in the right direction.tnx.

350zTT

04-05-08, 02:48 PM

can anyone shed light on this? or at least a link in the right direction.tnx.

Karos,

I guess we are all looking for answers. If you haven't found it yet, I simply took one of my small guitar cables (dual 1/4 inch cable) and loop the Left output (located in the rear of theMobile-pre and attach it to the front instrument in. Then run "sound system calibration" from the "Audio I/O" drop down on the top left of the TrueRTA GUI. Watch the squigly line go strait. I have 1/24 resolution and there are about 4 ultra small dips that wont correct. but in any other resolution its a perfect line. See if this helps you.:D

I have the older mobile-pre which has 1/4 inch outs and in and zero RCA. If you have RCA use an Radio Shack adapter to do the same thing. I used the left channel out since that is default.

I used the correction file that was listed at the begining of the thread for the Behringer ECM8000 and all seems fine. I am using it to tune an audiocontrol DQXS 1/3 octave EQ.

I hope sharing this will help someone. :o

350zTT

04-05-08, 03:44 PM

can anyone shed light on this? or at least a link in the right direction.tnx.

Karos,

I failed to mention to set your level so that the signal light is blinking and you don't clip to constatly (red light). I had to turn mine all the way up to allow the correction to work properly.

I also wanted to help anyone to find a clean and perfect Pink Noise generator. I found a free one offered off the audiocontrol website. All the places I looked and it was there all the time!!!! Here is the location. h**p://www.mobileaudiocontrol.com/whatsnew_detail.asp?id=845(they wont let me link till I have posted a while?!?!?!) I found a free converting utility off Download.com. The free version only saved 60% of the track so I burned it over and over to fill one cd with about 1/2 our of pink noise so I can do my tuning. I forget the name of the program since I am in my garage on my laptop, if you can't find it I iwll post it at a later time. VERY ACCURATE PINK NOISE. :p

MbayAQ

09-09-08, 03:52 AM

Would this work as a USB laptop sound card for this application or is it too crappy?

http://www.electronics-batteries.com/computer_speakers_dekcell_cpa_1037.htm

Or this?

http://cgi.ebay.com/USB-6-Channel-5-1-PCI-External-Sound-Card-PC-Laptop-A14_W0QQitemZ160241157621QQihZ006QQcategoryZ108984QQtcZphoto QQcmdZViewItem?refid=store

MbayAQ

09-11-08, 08:29 PM

Wow nobody knows? That's too bad...

Kal Rubinson

09-11-08, 08:43 PM

MbayAQ

09-11-08, 08:49 PM

I use an external USB sound box but not one of those.
Which one do you use?

Kal Rubinson

09-11-08, 08:50 PM

Which one do you use?Among others, the M-Audio MobilePre.

MbayAQ

09-11-08, 08:51 PM

Among others, the M-Audio MobilePre.

Are there any recommended ones under $100?

Kal Rubinson

09-11-08, 09:00 PM

Are there any recommended ones under $100?Dunno.

BTW, the small one does not have any info about input, only outputs, so I am not optimistic about it for this application. The other one looks like it would work.

MbayAQ

09-11-08, 10:19 PM

The other one looks like it would work.

Alright well I'll give it a try and report my results back here if anyone else is interested.

bikinpunk

10-12-08, 12:06 PM

I've been trying to figure this out for weeks...

I'm trying to use the oscilloscope function in TRTA so I can check for clipping out of amplifiers in my car stereo. Signal is split up via a preamp DSP, then sent out to separate amps for powering midbass/midrange/tweeter. Don't let the term 'car audio' scare you off; it's the same as if you were running dedicated preamp/amps in your home. ;)

I've got m-audio's mobilepre and a behringer ecm8000. My issue is the actual connection of wires and how to start this off. If anyone can help explain this, I'd really appreciate it. If you could do a simple MS Paint diagram that'd be very nice, too.

http://beonbeat.com/library/MobilePre_USB_callouts.jpg

mandarax

12-03-08, 10:29 AM

Has anyone compared the results of this program with an established well known instrument to see what the differences in measurements may or maynot be.. I would like to try and goof around with this software and maybe do a comparison if it has not already been done.

jmalto

12-05-08, 09:25 PM

rob r.

12-07-08, 05:57 AM

I have a few questions I hope someone can answer.

I am using a Creative Labs X-FI Express Notebook card (goes into the Express 54 slot) and I absolutely have tried everything to get a flat response during the calibration test and while I have come VERY close, it is not perfect. Does anyone have this card that can give some pointers?

I am primarly using TrueRTA with an external bass sweep CD that I have to plot my room frequency response. Does it even matter that I cannot get a flat response if I am not using TrueRTA's internal test tones? Should I be changing the Line-In back to Microphone once I plug my MIC into my sound card? The MIC I am using has a 1/4 plug that plugs directly into the soundcard, much like the ones you receive with an Onkyo or Denon receiver during an autosetup. If I leave the soundcard set to Line-In it barely pics up any sound at all in TrueRTA with my MIC. If I change the XFI to the Microphone from Line-in TrueRTA picks up sound fine and has roughly 24 DBA worth of background noise. I want to make sure this is the proper method or if I am setting this up wrong because I do not see the point of setting up TrueRTA with Line-in if you change it to Microphone to do the tests.

Once everything is setup and calibrated, does it matter if you move your sound sliders or must they be where you calibrated TrueRTA at?

Thanks for any help in advance, this is really confusing since I am not using TrueRTA's test tones or the USB sound card everyone else is.
All,

While RTA's are proven useful for generalized checks, they can't be depended on for equalization, that is, unless you're in an anechoic environment, your crossover/speaker combination sums to unity and demonstrates constant directivity.

Discrete echo's caused by the baffle and room boundaries can generate non-minimum phase aberations that can't be repaired with minimum phase (normal) equalization.

A useful tool will include a coherence test so that you may see which spectrum are non-minimum phase or, unequalizable.

In reality, minimum phase EQ is useful for matching the loudspeakers to each other. If you've ever done this you know this is perhaps one of the single most important procedures for proper imaging.

The procedure is simple. Place loudspeakers face to face. Set one out of polarity. Feed both a common signal. Equalise one speaker for maximum null. For 5 or 7 channel systems, use one speaker as the "reference" speaker and match the others to it.

Simple and effective.

A mentor of mine, the late, great Dr. Richard C. Heyser once said, "It pains me to give away in fifteen minutes what it took mefifteen years to discover."

rob r.

(yes, if you ask me what time it is, I'll tell you how to build a watch :D)