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post #901 of 3678
2/2/13 at 8:50am
Quote:
Originally Posted by AustinJerry View Post

It is not clear to me how a USB mic would operate properly without the calibration step, so my understanding is that an SPL is required.  Keep in mind that an SPL is a pretty important part of any audiophile's toolkit, and there are many times when you will benefit from having the SPL to take a quick measurement.  It is money well spent.
I am unclear on the need to know the true SPL using REW especially if as you correctly say, we will have other means to set the levels correctly (i.e. SPL meter or AVR's auto-eq system). When looking at something like frequency response, what matters is the relative amplitude of different frequencies. What their absolute value is, is unimportant for that kind of analysis. When someone posts such a graph here, I perform the same relative analysis. Ditto for the hundreds of measurements if not more that I have done with REW.

Am I missing a usage here that you all have discovered?
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post #902 of 3678
2/2/13 at 10:32am
Quote:
Originally Posted by amirm View Post

I am unclear on the need to know the true SPL using REW especially if as you correctly say, we will have other means to set the levels correctly (i.e. SPL meter or AVR's auto-eq system). When looking at something like frequency response, what matters is the relative amplitude of different frequencies. What their absolute value is, is unimportant for that kind of analysis. When someone posts such a graph here, I perform the same relative analysis. Ditto for the hundreds of measurements if not more that I have done with REW.

Am I missing a usage here that you all have discovered?
Dido.

This is a point worth bringing up, since I intend to measure frequency response for finding out what issues I have and how big they are, so I can acoustically treat a room for a smooth response.
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post #903 of 3678
2/2/13 at 12:11pm
Quote:
Originally Posted by amirm View Post

I am unclear on the need to know the true SPL using REW especially if as you correctly say, we will have other means to set the levels correctly (i.e. SPL meter or AVR's auto-eq system). When looking at something like frequency response, what matters is the relative amplitude of different frequencies. What their absolute value is, is unimportant for that kind of analysis. When someone posts such a graph here, I perform the same relative analysis. Ditto for the hundreds of measurements if not more that I have done with REW.

Am I missing a usage here that you all have discovered?

I too see no need for knowing absolute levels under most circumstances and the need for a "cr@ppy" Rat Shack SLM has prevented me from doing much with REW.
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post #904 of 3678
2/2/13 at 12:57pm
Quote:
Originally Posted by Theresa View Post

I too see no need for knowing absolute levels under most circumstances and the need for a "cr@ppy" Rat Shack SLM has prevented me from doing much with REW.

Apart from the characteristics of our ears that change FR as a function of level (refer to equal loudness curves), a microphone will always measure FR equally regardless of the strength of the test signal and will render a valid FR curve as long as it is above the noise floor but still does not enter clipping zone causing distortion in amp or speakers or both. Arbitrary level settings will also influence waterfall and spectrogram diagrams making them difficult for evaluation in case test signals are too low. REW does an automatic check-up and gives either a level OK confirmation or a level not-OK warning.

Precisely calibrated levels will become most important when we want to measure the effects of Audyssey's DynamicEQ or THX Loudness Plus, etc.
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post #905 of 3678
2/2/13 at 1:59pm

I took the question of the mic calibration step over to the HTS site, and here is the response I received:

 

"The SPL meter in REW has no idea what mic and sound card you are using and is designed to work with a wide range of devices. In order to be useful it needs a reference point for your particular setup. Of course, if you have a calibrated mic and have entered that calibration file then you've given REW a reference point (at all frequencies in the calibration file) and hence you do not need to provide another."

 

So, I stand corrected, and this eliminates the requirement for a SPL meter.

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post #906 of 3678
2/2/13 at 2:08pm
Quote:
Originally Posted by AustinJerry View Post

I took the question of the mic calibration step over to the HTS site, and here is the response I received:

"The SPL meter in REW has no idea what mic and sound card you are using and is designed to work with a wide range of devices. In order to be useful it needs a reference point for your particular setup. Of course, if you have a calibrated mic and have entered that calibration file then you've given REW a reference point (at all frequencies in the calibration file) and hence you do not need to provide another."

So, I stand corrected, and this eliminates the requirement for a SPL meter.

Oooops Jerry, I think we need to clarify the difference between level calibration and FR calibration (by way of a cal file), don't we? cool.gif
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post #907 of 3678
2/2/13 at 2:25pm
Quote:
Originally Posted by mogorf View Post

Oooops Jerry, I think we need to clarify the difference between level calibration and FR calibration (by way of a cal file), don't we? cool.gif

Just to clarify, I thought that the SPL tool in REW wasn't sufficient to get an absolute sound level from the UMM-6, even with the calibration file, and an external one (i.e. Radio Shack) was necessary to conduct this accurately? Correct me if I'm wrong, but I thought that was the understanding from Jason?

Also, I just got my UMM-6 mic from Cross Spectrum this afternoon, but was going to pick up the Radio Shack meter before moving forward. And BTW, I successfully got the HDMI connection to work with my Denon 4311 with all eight channels being displayed in REW on a" Denon-AVP" display. The trick wasn't to use Realtek, but the Geoforce Graphics card that came with my Dell (i.e. enable the digital audio on that device in Windows 7) to control HDMI.

I did have to download the latest driver for Geoforce and physically switch the display from Intel to Geoforce, and to avoid display resolution issues on my VT50, designate my laptop display as primary for multiple display options.
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post #908 of 3678
2/2/13 at 2:59pm
Quote:
Originally Posted by mogorf View Post


Oooops Jerry, I think we need to clarify the difference between level calibration and FR calibration (by way of a cal file), don't we? cool.gif

 

Feri, our discussion has nothing to do with the external calibration file, only whether the SPL tool in REW is required to set an absolute level for the mic.  I'm going to conduct some additional tests this evening, because I am still not convinced we understand the issue completely.

 

@Stuart, could you take a few screen shots describing the steps you took to get your laptop to recognize the Denon?  I am not following it completely.


Edited by AustinJerry - 2/2/13 at 4:13pm
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post #909 of 3678
2/2/13 at 4:34pm

OK, I ran a few tests to try and clarify the requirement for a microphone level calibration.

 

First of all, it you attempt to run a measurement without having run the microphone level calibration, you get this warning:

 

 

To me, this is an indication that it might be a good idea to calibrate.  For testing, I clicked "Continue anyway".

 

To review, there are several volume controls that affect the measurements.  They are:

 

- The Windows Audio playback device level (recommended level is 100%)

- The Windows Audio microphone level (ball-park level is 75%)

- The Master Volume on the AVR (no recommended level--it can be anything you want)

 

So, without calibrating the microphone, I ran several measurements:

 

 

 

 

The black line is with MV -30, the red line is with MV -15, the green line is is with Windows Audio Recording volume at 25% (instead of 75%), and finally, the blue line is after I calibrated the mic to a level of 80dB.

 

The point is, depending on where you set the AVR MV, or the Windows Audio levels, the vertical positioning of the measurement line is affected, but not the shape of the measurement itself.  So, Amir is correct in saying that calibrating the microphone volume does not affect the relative measurements.

 

However, repeatability is important, so once you determine the combination of Windows Audio level settings and AVR MV setting that results in measurements displayed where you want them. remember the settings and use the same ones every time.

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post #910 of 3678
2/2/13 at 5:17pm

That's interesting about the SPL not calibrated dialog box.  I'm 99.9% certain I didn't get that message when I ran my measurements with my OM mic.

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post #911 of 3678
2/3/13 at 3:42am
Quote:
Originally Posted by jkasanic View Post

That's interesting about the SPL not calibrated dialog box.  I'm 99.9% certain I didn't get that message when I ran my measurements with my OM mic.

You're right, it does not prompt with that message with OM mic anymore for me either.
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post #912 of 3678
2/3/13 at 3:44am
Quote:
Originally Posted by AustinJerry View Post

OK, I ran a few tests to try and clarify the requirement for a microphone level calibration.

 

First of all, it you attempt to run a measurement without having run the microphone level calibration, you get this warning:

 

 

To me, this is an indication that it might be a good idea to calibrate.  For testing, I clicked "Continue anyway".

 

To review, there are several volume controls that affect the measurements.  They are:

 

- The Windows Audio playback device level (recommended level is 100%)

- The Windows Audio microphone level (ball-park level is 75%)

- The Master Volume on the AVR (no recommended level--it can be anything you want)

 

So, without calibrating the microphone, I ran several measurements:

 

 

 

 

The black line is with MV -30, the red line is with MV -15, the green line is is with Windows Audio Recording volume at 25% (instead of 75%), and finally, the blue line is after I calibrated the mic to a level of 80dB.

 

The point is, depending on where you set the AVR MV, or the Windows Audio levels, the vertical positioning of the measurement line is affected, but not the shape of the measurement itself.  So, Amir is correct in saying that calibrating the microphone volume does not affect the relative measurements.

 

However, repeatability is important, so once you determine the combination of Windows Audio level settings and AVR MV setting that results in measurements displayed where you want them. remember the settings and use the same ones every time.

 

I can't see what the fuss is about, personally. It takes a few seconds to do what REW itself tells you to do in that dialog box you captured. Almost all of us have SPL meters, and for those who don't (Theresa ;)) the cost is negligible as a percentage of our total system cost. And, as you have said more than once, a SPL meter is a darned handy tool to own anyway.

 

So whatever anyone says, anywhere, I will still be taking the few seconds to match REW with my SPL meter - that way I know I cannot possibly go wrong, regardless of which 'theory' is gaining ground on any particular day, from any particular member.

 

I would commend my method to all :)

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post #913 of 3678
2/3/13 at 3:51am
Quote:
Originally Posted by amirm View Post

Quote:
Originally Posted by djbluemax1 View Post

Although we're aware that for new users, the "Audyssey killed my bass" comment is often due to not being used to flat bass...
You definitely make a good point that people who have never optimized low frequencies in their room can have the impression that the correct bass performance is not right. Whether it is by use of EQ or acoustic products, reduction of resonances (peaks) in the low frequency response will take away low frequency energy and with it, give the impression of less bass. This is especially felt in movies where the reduction in ringing (notes lasting longer than they should) can reduce what one feels in addition to hears. Hopefully they notice the better performance with tighter low frequency notes.

That said, we have to be careful to not take the lead from Audyssey and/or going by our gut feeling that "flat" response is the correct one. It is not perceptually nor based on research in the field.

Think about our everyday lives. We live in closed environments that don't remotely resemble an anechoic chamber. As such, the sounds that we hear are all benefiting from "room gain," i.e. exaggeration of low frequencies. Let's agree that it doesn't get higher fidelity than hearing those sounds as is. Recording them, then taking out the effects of the room gain when we play them by flattening the response will therefore degrade from our memory of what the real sound is like.

Here is a set of published measurements performed on a number of "room eq" systems with the overall double blind subjective listening test results overlaid on them:

image?pagenumber=24&w=800

The dashed black line in the middle is the room response with no EQ. We see the room gain in the form of that peak around 50 Hz. Notice the system in the bottom in teal which did exactly what you said: flat response in bass. Now notice the winning systems at the top. None of them used flat response. They had a tilting curve where the bass output was distinctly higher than the frequencies higher than them. We see clear correlation between doing that and subjective scores and verbal feedback from listeners. This was across 6 listeners and the outcome was consistent across all of them. Here is the break down on per frequency basis:

image?pagenumber=18&w=800

We see that they indeed voted RC6 and RC5 that aimed for flat response as having too little bass. Again these are trained listeners and not newbies.

Net, net, the goal as you use REW to optimize your system should be to get a *smooth* response, not *flat*. We crave more low frequencies than flat response gives us. The more precise way to say what you are saying then is that we like to see a smooth response, not flat.

Stepping up a few levels, we should keep in mind that correlation between acoustic measurements and what we like can range from very good to absolutely dreadful. While low frequency measurements are in the "very good" range of that spectrum, there can be surprises like above.

Again, you made a good point regarding correct bass and hopefully I did not take away from it by expanding the point smile.gif.
Yes, I'm familiar with the Harman curve and tests. It's one of the reasons I've considered XT32 Pro, for the curve editor, but there doesn't appear to be quite enough range in the adjustments. DEQ produces a similar effect, but not quite.

Many untrained listeners though, tend to gravitate towards a house curve with a seriously boosted low end, that far exceeds the Harman Preferred Curve.


Max
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post #914 of 3678
2/3/13 at 3:57am
Quote:

Originally Posted by AustinJerry View Post

 

The point is, depending on where you set the AVR MV, or the Windows Audio levels, the vertical positioning of the measurement line is affected, but not the shape of the measurement itself.  So, Amir is correct in saying that calibrating the microphone volume does not affect the relative measurements.

 

However, repeatability is important, so once you determine the combination of Windows Audio level settings and AVR MV setting that results in measurements displayed where you want them. remember the settings and use the same ones every time.

 

I think that is the best reason of all to perform this simple, one-off, additional step. The relative levels might not be affected but the measurements will be all over the place if the SPL used is different each time and comparing graphs will be made that much more difficult.

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post #915 of 3678
2/3/13 at 4:09am
Quote:
Originally Posted by kbarnes701 View Post

I can't see what the fuss is about, personally. It takes a few seconds to do what REW itself tells you to do in that dialog box you captured. Almost all of us have SPL meters, and for those who don't (Theresa wink.gif) the cost is negligible as a percentage of our total system cost. And, as you have said more than once, a SPL meter is a darned handy tool to own anyway.

So whatever anyone says, anywhere, I will still be taking the few seconds to match REW with my SPL meter - that way I know I cannot possibly go wrong, regardless of which 'theory' is gaining ground on any particular day, from any particular member.

I would commend my method to all smile.gif


you use the SPL meter to set the relative gain of each SOURCE to be consistent across the board; but it does not imply that the SPL is in any way accurate with respect to the ambient noise floor (unless calibrated and often done so with respect to the listening environment).
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post #916 of 3678
2/3/13 at 9:27am
Quote:
Originally Posted by AustinJerry View Post

@Stuart, could you take a few screen shots describing the steps you took to get your laptop to recognize the Denon?  I am not following it completely.

Will do, once I get a project deadline met. Sadly today's a work day until the Super Bowl...
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post #917 of 3678
2/3/13 at 10:04am
Quote:
Originally Posted by localhost127 View Post

Quote:
Originally Posted by kbarnes701 View Post

I can't see what the fuss is about, personally. It takes a few seconds to do what REW itself tells you to do in that dialog box you captured. Almost all of us have SPL meters, and for those who don't (Theresa wink.gif) the cost is negligible as a percentage of our total system cost. And, as you have said more than once, a SPL meter is a darned handy tool to own anyway.

So whatever anyone says, anywhere, I will still be taking the few seconds to match REW with my SPL meter - that way I know I cannot possibly go wrong, regardless of which 'theory' is gaining ground on any particular day, from any particular member.

I would commend my method to all smile.gif


you use the SPL meter to set the relative gain of each SOURCE to be consistent across the board; but it does not imply that the SPL is in any way accurate with respect to the ambient noise floor (unless calibrated and often done so with respect to the listening environment).

 

Not sure what you are saying LH - are you agreeing with Amirm (!) that there is no purpose in calibrating REW to a given SPL by using an independent meter, or agreeing with me that as it is a trivial step, and one apparently recommended by REW, there is no point in NOT doing it?  Or, of course, a third position which has escaped me (highly possible)?

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post #918 of 3678
2/3/13 at 10:30am
Thanks AustinJerry for the great doc. I have used REW a few times the over the last year, but with the whole analog output method. With your "how-to" doc, I was able to get my laptop hdmi configured no problem, with 8 channels.
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post #919 of 3678
2/3/13 at 12:06pm
Ok Guys, now that we have clarified that there are two kinds of calibrations involved with REW, namely:

1. Microphone calibration file that takes care of frequency response of the test mic, and

2. System level calibration of REW,

we can discuss how to calibrate #2, i.e. system level.

Open REW:



Click on the icon second from left called "SPL Meter".

You get this:



Please note, I'm doing the screen shots on another PC that is not in my HT living room, so the dB values are only for demo purposes.

Now click on Record (red button on the lower right side):



Then click on "Calibrate" (easy to find) and you immediately get this pop-up panel:



Click OK, then you will see this:



Then all you need to do is set the dB value until it matches the reading on your SLP meter and you're finished:



Let's not confuse "SPL meter", in this case it's not the separate Radio Shack device, but the built-in "SPL meter " of REW.

So, finally, nobody really needs to have a separate RadioShack SPL meter to calibrate REW measurement levels, ...well, ...maybe only Keith, eh? smile.gif

P.s.. Please only argue with me if you have valid points with reasoning. No red herings allowed. LOL
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post #920 of 3678
2/3/13 at 12:23pm
Quote:
Originally Posted by mogorf View Post

P.s.. Please only argue with me if you have valid points with reasoning. No red herings allowed. LOL

 

You're calibrating the mic using the same mic?  I thought the definition of calibrating was that you measured one instrument against a known standard?  What exactly is being calibrated here?  I think I'll stick with the way REW recommends it - I already have the SPL meter so it's no trouble to use it.


Edited by kbarnes701 - 2/4/13 at 4:08am
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post #921 of 3678
2/3/13 at 12:27pm
Quote:
Originally Posted by kbarnes701 View Post

You're calibrating the mic using the same mic?  I thought the definition of calibrating was that you measured one instrument against a known standard?  What exactly is being calibrated here?  I think I'll stick with the way REW recommends it - I already have the SPL meter so it's no trouble to use it.

Try the method described above Keith and compare it to "your way". Report back your findings please.smile.gif
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post #922 of 3678
2/3/13 at 1:38pm
Quote:
Originally Posted by mogorf View Post


Try the method described above Keith and compare it to "your way". Report back your findings please.smile.gif

Sorry, Feri, it doesn't work the way you describe.  The sound level displayed by the REW SPL meter when you press the red record button is dependent on having been calibrated to a known external sound level before it will display a proper value.  Take this test, for example:

 

- I set the AVR master volume to a value of -14, which on my system produces an 80dB sound level at the MLP (I know this because I have been doing this a long time).

- I launch REW and make sure everything in Preferences is configured properly.

- I then launch the REW SPL, and start the calibration tone.

- The REW SPL meter is reading 63dB, so (according to your instructions) I enter 63dB into the SPL Reading Calibration box and click Finished.

- Now I run the calibration tone again, and this time the SPL reads 63dB.  So, like your say, we have synchronized REW with itself.

- Now, since I know that the test tone is really playing at 80dB, I enter 80dB into the SPL Reading Calibration box, and click finished.

- Now I run the calibration tone a third time, and now the REW SPL shows 80dB.

 

So, how does the REW SPL show two completely different SPL readings, 63dB and 80dB, when the loudness of the test tone playing through the AVR has stayed the same?  It's because the reading on the SPL is dependent on the mic being calibrated.  Since I knew the tone was really 80dB, and calibrated REW properly, the SPL now reads 80dB, which is correct.

 

So, my friend, a very nice try, but your method involves circular logic (or circular calibration, as the case may be).  An external SPL is still required for proper calibration.  Thanks for sticking with me on this, Keith.

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post #923 of 3678
2/3/13 at 2:00pm
Quote:
Originally Posted by AustinJerry View Post

Sorry, Feri, it doesn't work the way you describe.  The sound level displayed by the REW SPL meter when you press the red record button is dependent on having been calibrated to a known external sound level before it will display a proper value.  Take this test, for example:

- I set the AVR master volume to a value of -14, which on my system produces an 80dB sound level at the MLP (I know this because I have been doing this a long time).


Oh my dear Jerry, if you have the MV on your AVR set to -14 dB you should not get 80 dB SLP at the MLP!!! Altough you did not specify what the input level is in this case! biggrin.gif

0 dB MV setting means you should get a 75 dB SPL at the MLP with a test tone at -30 dBfs. Now, turn it down to -14 dB and you get an SPL at the MLP at 75 -14 = 61 dB, right?

BTW, REW has it's own internal calibrated known sound level, so no need for an external known level source in this case.
Edited by mogorf - 2/3/13 at 2:17pm
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post #924 of 3678
2/3/13 at 2:27pm
Quote:
Originally Posted by mogorf View Post


Oh my dear Jerry, if you have the MV on your AVR set to -14 dB you should not get 80 dB SLP at the MLP!!! Altough you did not specify what the input level is in this case! biggrin.gif

0 dB MV setting means you should get a 75 dB SPL at the MLP with a test tone at -30 dBfs. Now, turn it down to -14 dB and you get an SPL at the MLP at 75 -14 = 61 dB, right?

BTW, REW has it's own internal calibrated known sound level, so no need for an external known level source in this case.

 

 

I have no idea what you are talking about, Feri, but you are wrong.  To settle this once and for all, I have received the following response on the HTS Forum from John, the author of REW:

 

"The UMIK-1 cal file includes a sensitivity figure which REW can use, along with the Windows mic volume setting, to know what the actual SPL in the room is. For other mics the SPL Level Calibration is needed to tell REW how the signal level it sees relates to actual SPL, and that calibration remains valid only if the input path gain remains the same (i.e. input volume setting is not altered, preamp gain not altered if using a preamp)."

 

Case closed.  You may read the post here:  http://www.hometheatershack.com/forums/rew-forum/65260-using-usb-mics-hdmi-several-questions.html#axzz2JsRELEV1

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post #925 of 3678
2/3/13 at 2:34pm
I apologise in advance if this has already been covered, but has anyone made a step-by-step tutorial on how to get the USB mic to work with REW with little to no hassles?
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post #926 of 3678
2/3/13 at 2:36pm
Quote:
Originally Posted by mogorf View Post

Quote:
Originally Posted by AustinJerry View Post

Sorry, Feri, it doesn't work the way you describe.  The sound level displayed by the REW SPL meter when you press the red record button is dependent on having been calibrated to a known external sound level before it will display a proper value.  Take this test, for example:

- I set the AVR master volume to a value of -14, which on my system produces an 80dB sound level at the MLP (I know this because I have been doing this a long time).


Oh my dear Jerry, if you have the MV on your AVR set to -14 dB you should not get 80 dB SLP at the MLP!!!

0 dB MV setting means you should get a 75 dB SPL at the MLP with a test tone at -30 dBfs. Now, turn it down to -14 dB and you get an SPL at the MLP at 75 -14 = 61 dB, right?

BTW, REW has it's own internal calibrated known sound level, so no need for an external known level source in this case.
Feri, don't misunderstand this as folks ganging up on you, but boiling this whole issue down to you last sentence about REW having its own calibrated sound level and therefore, not needing an external known level source:

Let's take, for example, system A) setup with Audyssey in a room with 98db/w/m speakers powered by the 100wpc receiver. MLP 10' away. Audyssey set it up with a -30db test tone so it SHOULD read 75db at the MLP. With the speakers sensitivity, the avr can hit THX Reference at the MLP, but you don't know the microphone's sensitivity. You also don't know the soundcard's input sensitivity or range. You don't know what the playback level in Windows was set at, or the input trim/gain.

How can you tell if what REW thinks is being output at 75db actually is being measured at 75db at the MLP? What if the speakers have an 88db/w/m sensitivity and the avr has 100wpc with no Audyssey to even try to calibrate the system to a known Reference?

There's no reference point anywhere in there. That's where using a separate meter allows calibrating to a known value.


Max
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post #927 of 3678
2/3/13 at 2:40pm
Quote:
Originally Posted by mogorf View Post

Quote:
Originally Posted by kbarnes701 View Post

You're calibrating the mic using the same mic?  I thought the definition of calibrating was that you measured one instrument against a known standard?  What exactly is being calibrated here?  I think I'll stick with the way REW recommends it - I already have the SPL meter so it's no trouble to use it.

Try the method described above Keith and compare it to "your way". Report back your findings please.smile.gif

 

Jerry beat me to it!

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post #928 of 3678
2/3/13 at 2:41pm
Quote:
Originally Posted by goneten View Post

I apologise in advance if this has already been covered, but has anyone made a step-by-step tutorial on how to get the USB mic to work with REW with little to no hassles?

 

Please open the link in my signature.  We will look forward to your feedback.

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post #929 of 3678
2/3/13 at 2:42pm
Quote:
Originally Posted by AustinJerry View Post


I have no idea what you are talking about, Feri, but you are wrong.  To settle this once and for all, I have received the following response on the HTS Forum from John, the author of REW:

"The UMIK-1 cal file includes a sensitivity figure which REW can use, along with the Windows mic volume setting, to know what the actual SPL in the room is. For other mics the SPL Level Calibration is needed to tell REW how the signal level it sees relates to actual SPL, and that calibration remains valid only if the input path gain remains the same (i.e. input volume setting is not altered, preamp gain not altered if using a preamp)."

Case closed.  You may read the post here:  http://www.hometheatershack.com/forums/rew-forum/65260-using-usb-mics-hdmi-several-questions.html#axzz2JsRELEV1

Tell me Jerry, in case of Audyssey setup, how does the Audyssey mic know how to set the speakers trims to reference level? Is there a need for a separate SPL meter or not? I can't remember anything mentioned in the setup guide to this extent! Case not closed, let's discuss till we can come to agreement! Deal?
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post #930 of 3678
2/3/13 at 2:43pm
Quote:
Originally Posted by mogorf View Post

Quote:
Originally Posted by AustinJerry View Post

Sorry, Feri, it doesn't work the way you describe.  The sound level displayed by the REW SPL meter when you press the red record button is dependent on having been calibrated to a known external sound level before it will display a proper value.  Take this test, for example:

- I set the AVR master volume to a value of -14, which on my system produces an 80dB sound level at the MLP (I know this because I have been doing this a long time).


Oh my dear Jerry, if you have the MV on your AVR set to -14 dB you should not get 80 dB SLP at the MLP!!! Altough you did not specify what the input level is in this case! biggrin.gif

0 dB MV setting means you should get a 75 dB SPL at the MLP with a test tone at -30 dBfs. Now, turn it down to -14 dB and you get an SPL at the MLP at 75 -14 = 61 dB, right?

BTW, REW has it's own internal calibrated known sound level, so no need for an external known level source in this case.

 

I think there are some of the famous red herrings in there Feri. Forget all that - if you take a test tone measurement with a SPL meter and set the AVR so it delivers a reading of 80dB, and then do it the way you suggested, the REW SPL meter will still be wrong and will not read 80dB. Why?  Because it hasn't been calibrated to the known reference level of 80dB.

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