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post #301 of 357 Old 06-17-2011, 06:31 AM
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Quote:
Originally Posted by Mark Strube View Post

This question may of been answered already, but I haven't seen it in a very clear manner, so I'm sorry if this is a repeat.

I have an Audix TM1, so I know my mic's response is very flat. I want to use this to EQ a room, but I wish to use the existing equipment's pink noise, instead of the noise from TrueRTA. I did some quick tests, and it seems to be reading levels much lower than it should. (Low SPL's for sounds that I know are much higher.)

I know the system calibration method, where you loop line in and line out, but that is only if you're going to be using TrueRTA's noise, correct?

How do I calibrate correct SPL if I'm only using the line in, and external pink noise? (I don't own an actual SPL meter right now, so I can't go that route, besides an app on my phone.)

Thanks!!



TrueRTA requires that you calibrate the on screen SPL readings. You use the SPL Calibration function. If you don't own an SPL meter, then you have no reference for the SPL calibration.

Note that you must recalibrate SPL any time you make a change in gain in your microphone to PC audio chain.

You don't need accurate SPL numbers to EQ, so don't let that stop you from doing whatever you are going to do.
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post #302 of 357 Old 06-17-2011, 12:07 PM
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Thank you for the reply! One more quick question: if I am not using RTA's noise (so I am not using any output audio from the laptop) is it better for me to not use system calibration , since that takes into account the sound card's output as well?

Thanks again!!
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post #303 of 357 Old 06-17-2011, 03:13 PM
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Quote:
Originally Posted by Mark Strube View Post

Thank you for the reply! One more quick question: if I am not using RTA's noise (so I am not using any output audio from the laptop) is it better for me to not use system calibration , since that takes into account the sound card's output as well?

Thanks again!!


You have to use the soundcard calibration file to make the TrueRTA FR curves flat.

The output and input calibration is similar to the SPL calibration. You only need to calibrate output and input levels if you need accurate dBu numbers.

Just as a note, I calibrate everything when and as needed. I also use a home made CD for my test soundtracks so I don't have to connect anything to my receiver.
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post #304 of 357 Old 06-17-2011, 06:54 PM
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Quote:
Originally Posted by Mark Strube View Post

I have an Audix TM1, so I know my mic's response is very flat. I want to use this to EQ a room, but I wish to use the existing equipment's pink noise, instead of the noise from TrueRTA. I did some quick tests, and it seems to be reading levels much lower than it should. (Low SPL's for sounds that I know are much higher.)

I don't see any mention there of a mic pre-amp. That mic requires a pre-amp and phantom power.

Regards,
Wayne A. Pflughaupt



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post #305 of 357 Old 06-18-2011, 02:00 AM
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My laptop has a "Mic" input and not a line in. I was only using a phantom power box and then directly into my Mic port, using an XLR -> minijack cable. Seemed to be receiving audio just fine, but only with incorrect SPL, mentioned earlier.

It's my understanding that if it's a Mic input jack, that has a preamp?
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post #306 of 357 Old 06-18-2011, 07:18 AM
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Correct, but if it doesn't have a gain control that would account for your SPL issue. Also, I wouldn't expect a computer's mic input to be terribly accurate, and it can't be calibrated. Keep in mind that your measurement accuracy will be no better than the weakest link in the signal chain. I expect you'd get better results with a legitimate pre-amp like the Behringer XENYX 502 or a combo USB audio interface/pre-amp like the M-Audio Mobile Pre or TASCAM US122 (to name a couple, there are plenty of similar products on the market). I mean, you've invested in a rather pricey mic for this, so it seems counter-productive to cheap out by using the computer mic input.

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post #307 of 357 Old 06-18-2011, 12:11 PM
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Thank you for the recommendation!! I like that the USB interface devices function as both a pre-amp and providing phantom power... for a really good price at that. I looked at both and I am leaning toward the M-AUDIO, is there any you'd recommend over another (cleanest audio?), or are they all pretty decent?

Also, just to be clear (sorry to be repetetive)... even though I won't be using any test tones from TrueRTA, it is still a good idea to do a system calibration? (Looping the line out into my input.) I thought I read somewhere that if I'm not using the tones from TrueRTA, doing that calibration can skew the numbers, since it's taking into account my computer's audio output. Is that at all true?
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post #308 of 357 Old 06-19-2011, 07:58 AM
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Quote:


I looked at both and I am leaning toward the M-AUDIO, is there any you'd recommend over another (cleanest audio?), or are they all pretty decent?

I’ve only used the TASCAM myself, so I can’t say. However, ”clean” isn’t really an issue for taking room measurements. It’s only relevant if you intend to use the interface for its intended purpose: Recording. If that’s the case, you should have no problem finding on-line user reviews to make that determination. That said, I think most of these things have amazingly flat response. For example, the US122, is down only 1/4 dB or so at 20 Hz, IIR. Technically it doesn’t even need a calibration file!

BTW - separate from that you should Google for some reviews to make sure any interface you’re interested in is compatible with your operating system. This post will give you some pointers in what to look for in the reviews.


Quote:


Also, just to be clear (sorry to be repetetive)... even though I won't be using any test tones from TrueRTA, it is still a good idea to do a system calibration? (Looping the line out into my input.) I thought I read somewhere that if I'm not using the tones from TrueRTA, doing that calibration can skew the numbers, since it's taking into account my computer's audio output. Is that at all true?

I don’t know a lot about the specifics of TruRTA, but I doubt the system calibration has anything to do with the test signals it generates. The purpose of the system calibration is to eliminate any inaccuracies in response that the sound card and mic have. It would be silly for the compensation to be built-in to the test signals. If that were the case, TruRTA would have to specify that the system could only be used with an XYZ sound card and ABC mic, would it not? Because using any others would render the system inaccurate.

With sound card and mic calibrations in place, any reliable test signal can be used. For instance, I’ve used the pink noise signal from my hardware AudioControl RTA to take measurements with a software program similar to TruRTA, and it works fine.

Hope that helps.

Regards,
Wayne A. Pflughaupt



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post #309 of 357 Old 06-19-2011, 10:26 AM
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Sorry I was a bit unclear with the question. Since I won't be using my sound card's audio output for these tests, but instead the pink noise built into the hardware I'm testing, would running the system calibration unnecessarily take into account imperfections in the sound card's output, which shouldn't be a part of the calculations, since it's not being used?
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post #310 of 357 Old 06-19-2011, 12:02 PM
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Quote:
Originally Posted by Wayne A. Pflughaupt View Post


Correct, but if it doesn't have a gain control that would account for your SPL issue. Also, I wouldn't expect a computer's mic input to be terribly accurate, and it can't be calibrated. Keep in mind that your measurement accuracy will be no better than the weakest link in the signal chain. I expect you'd get better results with a legitimate pre-amp like the Behringer XENYX 502

I have a Xenyx 502 that is available for a good price (I ended up going in a different direction). PM me if you are interested

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post #311 of 357 Old 06-19-2011, 04:54 PM
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Quote:
Originally Posted by Mark Strube View Post

Sorry I was a bit unclear with the question. Since I won't be using my sound card's audio output for these tests, but instead the pink noise built into the hardware I'm testing, would running the system calibration unnecessarily take into account imperfections in the sound card's output, which shouldn't be a part of the calculations, since it's not being used?

Even if you don't use the soundcard's output for generating test signals, the output circuitry is still being used to send the signal from the mic to the computer: E.g., mic -> mic pre-amp - > audio circuitry (gain stages, etc.) -> USB -> computer. So yes you still need the calibration file for the sound card.

But like I said, you may find that the response of the combo audio interface you choose is so good that it doesn't need a calibration file.

Regards,
Wayne A. Pflughaupt



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post #312 of 357 Old 06-19-2011, 05:29 PM
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Cool, thanks again for all the info.

So here's an interesting tidbit... if I run the calibration from the line out to mic in (no USB device involved)... the original EQ line is actually quite straight, and very close to being perfect. When I involve the M-Audio MobilePre in the calibration (line out -> XLR-in on MobilePre -> USB input), the original EQ line has a lot more variances (dips and spikes)... which is then corrected of course by the end of the calibration.

Correct me if I'm wrong, but this tells me that my existing sound card has some very flat response to begin with, which means that it isn't improperly coloring the EQ of the MobilePre much, if at all?
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post #313 of 357 Old 07-20-2011, 01:07 PM
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This question is probably better directed to Digidesign or the makers of my OS/laptop (MS & Dell), but I thought I'd throw it out there in case anyone's run across it.

Because I'm running XP, the guys at the local pro audio shop gave me a deal on an old Mbox1 that I'm trying to use as the pre/phantom for my dbx RTA-M mic. They installed the drivers for the mbox, along with a copy of Protools LE (vers 7.4). I'm seeing audio signal into protools, but not in the TrueRTA.

I'm pretty sure it's related to the following: on TrueAudio's FAQ page, under "Sound Card Questions", the first paragraph of the response to the first question has directions to tell Windows that I'm using an external sound system, by opening the "sounds and audio" control panel and clicking on the audio tab. While I can select the Mbox as the default playback device, it doesn't give me the option to select it as the recording device. The only option is the installed card ("Sigma Tel Audio").

This is my first foray into Protools (I'm mostly a live-sound guy) but my understanding is that this version (and therefore the Mbox?) won't work with post-XP OS's. My laptop does tend to be a bit "buggy" and obviously both it an the OS are pretty old. Still, it'd help me out quite a bit to get it running. Any help is appreciated.
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post #314 of 357 Old 09-10-2011, 12:06 PM
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Hello All,

I read Brent Butterworth article in S&V for DIY audio measurement and it has me interested in trying this. In Brent's article it seems a mic preamp was not necessary when using laptops internal sound card. From reading this thread it seems many recommend the preamp. Also it seems the EMM-6 mic has a built in preamp, how does this differ from the external preamp? If someone could elaborate further I would be grateful.

Thanks Bob
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post #315 of 357 Old 09-10-2011, 04:47 PM
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Mics require an external pre-amp; they don’t have built-in pre amps. If you’re using the Dayton EMM-6 or Behringer ECM 8000, they require phantom power, so a computer pre-amp won’t work.

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post #316 of 357 Old 09-10-2011, 07:08 PM
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What is the differnece between the M-Audio Mobile Pre USB and something like the Rolls MP13 Mini-Mic Preamp with Phantom Power? thanks for the help, Bob
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post #317 of 357 Old 09-10-2011, 07:41 PM
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The Mobile-Pre (and similar units) combine the mic pre-amp, phantom power and USB interface in a single package. With the Rolls you’d still need an additional USB sound card.

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post #318 of 357 Old 09-10-2011, 08:28 PM
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Brent’s article suggested the mic had a preamp, I knew it I read it somewhere. Must have been a misprint.
“The EMM-6 and ECM-8000 require phantom power: a separate DC supply that sends voltage up the cable to power the mike’s internal preamp.”
http://www.soundandvisionmag.com/art...ement?page=0,2

>With the Rolls you’d still need an additional USB sound card.<<br /> Unless you try to use the sound card in your laptop?

So I think I have it, Windows Laptop, EMM-6 , TrueRTA(1/6), M-Audio Mobile Pre and connecting cables. Laptop aside the price for those componets are pretty close to the complete Dayton OmniMic Package which I imagine is another alternative.

Thanks Bob
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post #319 of 357 Old 09-11-2011, 07:01 PM
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Some mic types such as ribbon and electrets do have built-in pre amps, but condenser mics (such as the EMM-6 and ECM-8000) do not.

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post #320 of 357 Old 11-15-2011, 02:07 PM
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Hi,

I hope you can help me out with this one:

I bought a new laptop and reinstalled TrueRTA on this one, but the mic signal is not being read. I've calibrated the soundcard and activated the (advised) mic calibration file for the Behringer ECM8000.

The mic works; I've tested it in other software with the same soundcard, so I'm a bit flabbergasted right now.

Please let me know if this sounds familiar and you know a solution.

Regards,

Charles
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post #321 of 357 Old 11-15-2011, 02:46 PM
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Solved it. Had to manually adress it in the Audio Device selection.
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post #322 of 357 Old 11-22-2011, 12:33 PM
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I'm trying to figure out if I can use equipment I already have to perform a RTA measurement. I have a Tritton AX 720 headphone that comes with a processor. One of the things this processor can do is act as a USB microphone to a PC. It has it's own power supply. I already have a radioshack SPL meter. Should this processor work with a laptop to perform the RTA measurement?

Here is a link that explains the unit in more detail.

http://www.jeffsreviews.com/Articles.../ax%20720.html
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post #323 of 357 Old 12-10-2011, 06:36 PM
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Hi guys,

I'm new to the forum. I've read all the posting here and I don't see anything regarding headphones.

I'm trying to set up a headphone tester at my home. At the lab, my guys use Clio, anechoic chambers, HATS and IEC711 mics. But that's just not in my budget. I'm looking to build a test jig so I can approximate and make some mods to headphones to tweak freq responses.

I can make the adapters to house the mic and couple to the IEM's and headphones etc. but I'm curious if anyone here has successfully been able to use TrueRTA with MobilePre/ECM8000 for this use.

Or if anyone has suggestions on what I might be able to source for a little DIY project, I'd greatly appreciate it!
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post #324 of 357 Old 12-11-2011, 10:47 PM
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Well, I spent the weekend researching and it seems there's no real workaround. I might have to pluck down $800 for a IEC 711 microphone if I want realistic FRs.
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post #325 of 357 Old 12-12-2011, 09:46 AM
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Quote:
Originally Posted by Y_audio View Post

I'm curious if anyone here has successfully been able to use TrueRTA with MobilePre/ECM8000 for this use.

If you already have ECM8000, put it next to the headphone (block the other side so it won't interfere) and see if it works.
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post #326 of 357 Old 01-13-2012, 10:36 AM
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Hi all,
First post in this forum, sure to not be the last. At the beginning of this thread there were some non-functional links to pictures of the proper wiring connections for Mobile Pro,(I think), for use with TruRTA. I am assuming these would be the same for the Tascam 122 that I will be using. Can anyone provide a working link? If not, a step by step explanation would be greatly appreciated. Please bear in mind that I am the epitome of those in need of the "Dummies" series of texts!

TIA,
Jim
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post #327 of 357 Old 01-13-2012, 03:14 PM
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This picture is for a different measurement platform, but the cabling / connections should be the same.

REW cabling basics


Regards,
Wayne A. Pflughaupt



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post #328 of 357 Old 01-13-2012, 03:55 PM
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That is perefect Wayne! Thank you!!
Jim
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post #329 of 357 Old 01-25-2012, 01:39 PM
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I got my M-Audio Mobile Pro (Generation 1) and trying to set it up on my lapto running Windows 7 Home Premiium 64bit and having a very strange behaviour.

Without anything connected to in or out , no mic no wire, nothing, just a usb cable, all gain controls on sound card are turned down to zero.

Now when I start the analyzer in TrueRTA I see a very high noise up to 70db, I will try to post the image.


Has anyone seen such behaviour? I did a calibration and that does not affect it? I have another PC (WIn 7 Ultimate 32 bit) with Audiotrak 7.1 HIFI PCI sound card and when I loop that card I can hardly see any noise there and it is below0 db when nothing is connected.
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post #330 of 357 Old 01-25-2012, 01:39 PM
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still trying with image
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