Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 16 - AVS Forum
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post #451 of 10744 Old 01-18-2013, 06:10 PM
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Looking forward to when the UMM-6 mic from Cross-Spectrum Labs arrives, it may have the same calibration files as I received with the EMM-6, which are described below.  Can enyone explain the difference between the "narrow band response" and the "one third octave band response" files?

 

 

Calibrated Dayton EMM-6 Data CD Contents

This CD contains the following data files:

 

narrow band response 0 degree.FRD (all microphones)

narrow band response 45 degree.FRD (Basic+ and Premium+ microphones only)

narrow band response 90 degree.FRD (Basic+ and Premium+ microphones only)

one third octave band response 0 degree.FRD (all microphones)

one third octave band response 45 degree.FRD (Basic+ and Premium+ microphones only)

one third octave band response 90 degree.FRD (Basic+ and Premium+ microphones only)

EMM-6 polar response CSL Ennn.xls (Premium and Premium+ microphones only)

EMM-6 polar response CSL Ennn.csv (Premium and Premium+ microphones only)

 

Frequency Response Files:

 

The narrow band response x degree.FRD files contain the narrowband (FFT) frequency response response calibration files for the microphone at an angle of 0 degree incidence (microphone pointed directly at the sound source), 45 degrees incidence (microphone pointed diagonally with respect to the sound propagation path of the source) and 90 degrees incidence (microphone perpendicular to the sound propagation path of the source).

 

The one third octave band response x degree.FRD files contain the one-third octave band frequency response response calibration files for the microphone at an angle of 0 degree incidence (microphone pointed directly at the sound source), 45 degrees incidence (microphone pointed diagonally with respect to the sound propagation path of the source) and 90 degrees incidence (microphone perpendicular to the sound propagation  path of the source).

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post #452 of 10744 Old 01-18-2013, 07:09 PM
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I have installed the software and am considering ordering the individually calibrated mike. I am also confused about the calibration connections.
I plan to use HDMI and the USB mike, however connections need to be set up to calibrate the sound card and to initially calibrate the mike.
The link to the external website seems to be more focused on the older version of REW. I also don't have a preout from my receiver for left or right speakers. Should I disconnect my zone 2 preouts and use those or should I hook up to the receiver headphone jack (more conveniently located in the front)? For someone who does not have any conversion pieces (so can start fresh), I'd be greatful for a short list of what to order or pick up in my situation for those two calibration requirements.
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post #453 of 10744 Old 01-18-2013, 07:52 PM
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Originally Posted by highmr View Post

I have installed the software and am considering ordering the individually calibrated mike. I am also confused about the calibration connections.
I plan to use HDMI and the USB mike, however connections need to be set up to calibrate the sound card and to initially calibrate the mike.
The link to the external website seems to be more focused on the older version of REW. I also don't have a preout from my receiver for left or right speakers. Should I disconnect my zone 2 preouts and use those or should I hook up to the receiver headphone jack (more conveniently located in the front)? For someone who does not have any conversion pieces (so can start fresh), I'd be greatful for a short list of what to order or pick up in my situation for those two calibration requirements.

 

In order to calibrate the soundcard, you simply need to feed the output from one channel back into the laptop's mic input.  For example, if you use the right channel to calibrate, then any output on your AVR that has the right channel signal will work.  So yes, I think the zone two right channel output can be used to calibrate the soundcard.

 

As per the guide linked in my signature, you will need a short cable that has a stereo mini-plug on one end (to connect to the mic input), and dual RCA plugs at the other end, one of which would connect to the AVR right channel zone two output.  Several earlier posts had pictures of such a cable.

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post #454 of 10744 Old 01-19-2013, 09:18 AM
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Even if you don't have a pre out your receiver probably has an analog "record out" type of output which will pass through an analog input signal. It might be labeled something like "DVR OUT" or "VCR OUT" or "Media Player" or something of the like.

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post #455 of 10744 Old 01-19-2013, 03:02 PM
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Quote:
Originally Posted by AustinJerry View Post

Quote:
Originally Posted by highmr View Post

I have installed the software and am considering ordering the individually calibrated mike. I am also confused about the calibration connections.

I plan to use HDMI and the USB mike, however connections need to be set up to calibrate the sound card and to initially calibrate the mike.

The link to the external website seems to be more focused on the older version of REW. I also don't have a preout from my receiver for left or right speakers. Should I disconnect my zone 2 preouts and use those or should I hook up to the receiver headphone jack (more conveniently located in the front)? For someone who does not have any conversion pieces (so can start fresh), I'd be greatful for a short list of what to order or pick up in my situation for those two calibration requirements.

In order to calibrate the soundcard, you simply need to feed the output from one channel back into the laptop's mic input.  For example, if you use the right channel to calibrate, then any output on your AVR that has the right channel signal will work.  So yes, I think the zone two right channel output can be used to calibrate the soundcard.

As per the guide linked in my signature, you will need a short cable that has a stereo mini-plug on one end (to connect to the mic input), and dual RCA plugs at the other end, one of which would connect to the AVR right channel zone two output.  Several earlier posts had pictures of such a cable.

Thanks AustinJerry and Batpig. I was confused about whether I also needed the Y cable to convert to two mono signals for either calibration task. I have a 2310. You are right, there are both DVR and VCR analog outs.
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post #456 of 10744 Old 01-20-2013, 05:08 AM
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Quote:
Originally Posted by AustinJerry View Post

In order to calibrate the soundcard, you simply need to feed the output from one channel back into the laptop's mic input.  For example, if you use the right channel to calibrate, then any output on your AVR that has the right channel signal will work.  So yes, I think the zone two right channel output can be used to calibrate the soundcard.

As per the guide linked in my signature, you will need a short cable that has a stereo mini-plug on one end (to connect to the mic input), and dual RCA plugs at the other end, one of which would connect to the AVR right channel zone two output.  Several earlier posts had pictures of such a cable.


I asked that question over at the Shack and John's reply was that you'd be better off not using a sound card calibration.

My issue with using the loop through in the laptop is that once you switch to the usb mic, you're no longer are using the same input which is what you used to do the sound card calibration. The previous instructions had to do with using an external usb card and doing the loop through through it.

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post #457 of 10744 Old 01-20-2013, 05:35 AM
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Hi Jim P. glad you brought this up. Was getting confused reading the last two pages if sound card calibration is necessary if using USB mic and HDMI connection.
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post #458 of 10744 Old 01-20-2013, 05:53 AM
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Quote:
Originally Posted by JimP View Post

Quote:
Originally Posted by AustinJerry View Post

In order to calibrate the soundcard, you simply need to feed the output from one channel back into the laptop's mic input.  For example, if you use the right channel to calibrate, then any output on your AVR that has the right channel signal will work.  So yes, I think the zone two right channel output can be used to calibrate the soundcard.

As per the guide linked in my signature, you will need a short cable that has a stereo mini-plug on one end (to connect to the mic input), and dual RCA plugs at the other end, one of which would connect to the AVR right channel zone two output.  Several earlier posts had pictures of such a cable.


I asked that question over at the Shack and John's reply was that you'd be better off not using a sound card calibration.

My issue with using the loop through in the laptop is that once you switch to the usb mic, you're no longer are using the same input which is what you used to do the sound card calibration. The previous instructions had to do with using an external usb card and doing the loop through through it.

 

I'm getting confused now. Do you mean that the normal input used for measuring will be the USB input on the laptop but the input used for the soundcard calibration will be the mic input on the laptop?

 

If so, then yes, I can see the point you are making... what's the point of calibrating the soundcard by using a different input to the one you will be suing for measuring?  If the USB mic on the USB input has any differences from the mic input, then the calibration will not be valid. So there's no point doing it.

 

Next question then is: how important is the sound card calibration step?  If it is OK for us to ignore it, then why is it not equally OK for everyone to ignore it?  The soundcard chip in my laptop likely cost a few cents - surely it is important to eliminate its characteristics by measuring and creating an inverse filter (which is what I assume happens)?

 

Did John give a reason other than the one you mention, or elaborate at all...?

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post #459 of 10744 Old 01-20-2013, 06:23 AM
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The sound card calibration instructions were intended for those of us who are using the Audyssey mic, plugged into the mic input on the laptop. I believe we have said several times that the guide will need to be revised once we have USB mics available for testing. Whether or not a sound card calibration will be required or not I cannot say at this time.
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post #460 of 10744 Old 01-20-2013, 06:29 AM
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Quote:
Originally Posted by AustinJerry View Post

The sound card calibration instructions were intended for those of us who are using the Audyssey mic, plugged into the mic input on the laptop. I believe we have said several times that the guide will need to be revised once we have USB mics available for testing. Whether or not a sound card calibration will be required or not I cannot say at this time.
Jerry,

That may be so, but in post 453 you were replying to someone who had stated that he'd be using a usb mic.

On the bright side, we're making progress on some of these finer points. smile.gif

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post #461 of 10744 Old 01-20-2013, 06:41 AM
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Quote:
Originally Posted by JimP View Post

Quote:
Originally Posted by AustinJerry View Post

The sound card calibration instructions were intended for those of us who are using the Audyssey mic, plugged into the mic input on the laptop. I believe we have said several times that the guide will need to be revised once we have USB mics available for testing. Whether or not a sound card calibration will be required or not I cannot say at this time.
Jerry,

That may be so, but in post 453 you were replying to someone who had stated that he'd be using a usb mic.

On the bright side, we're making progress on some of these finer points. smile.gif

 

Yes we are. I am hoping Jason is working on a step-by-step guide to using the mic once it arrives (unless you are taking on this mantle, Jerry?). From plugging in (with REW all set up to go as per Jerry's guide) to taking the first set of measurements, to generating some graphs, and to interpreting the results, and suggestions as to how to improve on them...

 

I'd like to know which speakers to measure, which combinations of speaker to measure, how many measurement positions to use, etc etc - and then take it from there.

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post #462 of 10744 Old 01-20-2013, 06:46 AM
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Quote:
Originally Posted by JimP View Post

Jerry,

That may be so, but in post 453 you were replying to someone who had stated that he'd be using a usb mic.

On the bright side, we're making progress on some of these finer points. smile.gif

I hear you, Jim. My intent was not to give bad advice. Configuring REW for a USB mic is uncharted territory for me. I trust we'll get it all worked out soon.

BTW, I sent a note to CSL, and they still don't have an ETA on the UMM-6 mics.
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post #463 of 10744 Old 01-20-2013, 06:47 AM
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Sound card calibration will most likely NOT be required if you plan to use the HDMI output direct to the AVR, as you will be staying in the digital domain right into the AVR. The 'cheap' sound card within the laptop becomes redundant.
When the analogue output (headphone) jack was used, then a cal file was required to compensate for its output characteristics.
The USB mics that we're all waiting for will include specific calibration files, so the complete loop should be as close to calibrated as makes no difference.
Regards, Mike.
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post #464 of 10744 Old 01-20-2013, 06:53 AM
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Quote:
Originally Posted by AustinJerry View Post

The sound card calibration instructions were intended for those of us who are using the Audyssey mic, plugged into the mic input on the laptop. I believe we have said several times that the guide will need to be revised once we have USB mics available for testing. Whether or not a sound card calibration will be required or not I cannot say at this time.



How do you do a soundcard calibration if you do not have a full duplex sound card?


Full duplex test:

http://www.ehow.com/how_7763496_check-sound-card-fullduplex.html
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post #465 of 10744 Old 01-20-2013, 08:19 AM
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Sound card calibration will most likely NOT be required if you plan to use the HDMI output direct to the AVR, as you will be staying in the digital domain right into the AVR. The 'cheap' sound card within the laptop becomes redundant.
When the analogue output (headphone) jack was used, then a cal file was required to compensate for its output characteristics.
The USB mics that we're all waiting for will include specific calibration files, so the complete loop should be as close to calibrated as makes no difference.
Regards, Mike.

 

Brilliant!  That is what I wanted to hear - the simpler the better for me.

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post #466 of 10744 Old 01-20-2013, 10:16 AM
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How do you do a soundcard calibration if you do not have a full duplex sound card?


Full duplex test:

http://www.ehow.com/how_7763496_check-sound-card-fullduplex.html

 

Because the output is on the HDMI interface, using a custom driver called ASIO4ALL.  You are correct when you say using the mic input and the headphone output simultaneously is not possible using the internal audio on a laptop.

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post #467 of 10744 Old 01-20-2013, 10:50 AM
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I am hoping Jason is working on a step-by-step guide to using the mic once it arrives (unless you are taking on this mantle, Jerry?). From plugging in (with REW all set up to go as per Jerry's guide) to taking the first set of measurements, to generating some graphs, and to interpreting the results, and suggestions as to how to improve on them...

I was planning on amending the guide to reflect the differences when using the USB mic. Once we have mastered configuring the new hardware and we are generating meaningful measurements, we will graduate to the real purpose of the thread--analyzing the results and discussing remedial solutions. This part will differ for each set of measurements, and I doubt there is a single cookbook approach to fixing issue can be documented. Of course, we are hoping Jason re-joins the thread and shares his knowledge.
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post #468 of 10744 Old 01-20-2013, 11:08 AM
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Quote:
Originally Posted by AustinJerry View Post

Quote:
Originally Posted by kbarnes701 View Post

I am hoping Jason is working on a step-by-step guide to using the mic once it arrives (unless you are taking on this mantle, Jerry?). From plugging in (with REW all set up to go as per Jerry's guide) to taking the first set of measurements, to generating some graphs, and to interpreting the results, and suggestions as to how to improve on them...

I was planning on amending the guide to reflect the differences when using the USB mic. Once we have mastered configuring the new hardware and we are generating meaningful measurements, we will graduate to the real purpose of the thread--analyzing the results and discussing remedial solutions. 

 

 

You are a star, Jerry.

 

 

Quote:
This part will differ for each set of measurements, and I doubt there is a single cookbook approach to fixing issue can be documented. Of course, we are hoping Jason re-joins the thread and shares his knowledge.

 

Point taken - but some sort of 50,000 foot view would be good - I think making the graphs will be the easy part. It is interpreting them that is the tricky part for newcomers to all this (and I class myself as that, even though I have some limited experience with OmniMic). A 101 on what to look for in the graphs (eg a dip at the XO frequency) and how to fix it, in broad terms, would be great.

 

I think we are on the same page - the thread will take on its own life once we all have mics.

 

And yes, I remember Jason.... ;)

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post #469 of 10744 Old 01-20-2013, 11:38 AM
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Jerry, been playing and practicing with speaker measurement following the excellent REW Guide. But getting clipping warning when performing sub measurement. On REW Guide page 33-36 would I need to re-do step 4 "Microphone Calibration" just to perform a sub measurement?
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Jerry, been playing and practicing with speaker measurement following the excellent REW Guide. But getting clipping warning when performing sub measurement. On REW Guide page 33-36 would I need to re-do step 4 "Microphone Calibration" just to perform a sub measurement?

 

Clipping indicates the mic level is too high.  Suggestions:  Lower the microphone volume in Windows audio (I use 60 as the volume setting).  Then re-calibrate the mic in REW, adjusting AVR volume to reach 80dB reading on the SPL held next to the mic, and then keying in 80dB in the calibration setting.  Then the measurement sweep should not cause clipping.

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post #471 of 10744 Old 01-20-2013, 12:07 PM
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re: soundcard calibration.

This is from my original experiences with REW:

Compaq Presario:

 

 

Mac mini:

 

 

Mobile Pre:

 

 

I will continue to use my RS meter and external card and Java, and will continue to wait eagerly for the rest of you to get your mics and start posting and discussing the resulting graphs.

 

In the meantime, here's my waterfall:

 

 

Hurry up, guys!

Michael


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Did you really need to quote that entire post in your reply?
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post #472 of 10744 Old 01-20-2013, 12:10 PM
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Quote:
Originally Posted by LastButNotLeast View Post

re: soundcard calibration.

This is from my original experiences with REW:

Compaq Presario:

 

 

Mac mini:

 

 

Mobile Pre:

 

 

I will continue to use my RS meter and external card and Java, and will continue to wait eagerly for the rest of you to get your mics and start posting and discussing the resulting graphs.

 

In the meantime, here's my waterfall:

 

 

Hurry up, guys!

Michael

That is actually a pretty good waterfall, Michael.  Do you have an ETC as well?

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post #473 of 10744 Old 01-20-2013, 12:24 PM
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Quote:
Originally Posted by AustinJerry View Post

That is actually a pretty good waterfall, Michael.  Do you have an ETC as well?

No, but I'll get it all hooked up again when you guys are up and running (and I have more of an idea of what we're all talking about!).

Thanks for letting me know I've stumbled in the right direction, though.

Sometimes dumb luck counts as much as raw talent.

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Did you really need to quote that entire post in your reply?
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post #474 of 10744 Old 01-20-2013, 01:05 PM
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Quote:
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That is actually a pretty good waterfall, Michael.  Do you have an ETC as well?

Jerry--for us waterfall younglings, can you explain why?

Stuart

 

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post #475 of 10744 Old 01-20-2013, 01:29 PM
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I guess now I am getting confused which is easy.

I have the USB mic along with using the HDMI. I am using the laptop and the built in sound card and I use the calibration file that came with the mini dsp email when I ordered the mic. Other than the issues with getting the 8 options as compared to the 2 and changing the speakers from stereo to 5.1, I don't recall having to do any sort of sound card calibration. Am I missing something?

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post #476 of 10744 Old 01-20-2013, 01:32 PM
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Quote:
Originally Posted by AustinJerry View Post

Quote:
Originally Posted by JChin View Post

Jerry, been playing and practicing with speaker measurement following the excellent REW Guide. But getting clipping warning when performing sub measurement. On REW Guide page 33-36 would I need to re-do step 4 "Microphone Calibration" just to perform a sub measurement?

 

Clipping indicates the mic level is too high.  Suggestions:  Lower the microphone volume in Windows audio (I use 60 as the volume setting).  Then re-calibrate the mic in REW, adjusting AVR volume to reach 80dB reading on the SPL held next to the mic, and then keying in 80dB in the calibration setting.  Then the measurement sweep should not cause clipping.

Another one for the FAQ...

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post #477 of 10744 Old 01-20-2013, 01:33 PM
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post #478 of 10744 Old 01-20-2013, 01:36 PM
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Quote:
Originally Posted by sdrucker View Post

Quote:
Originally Posted by AustinJerry View Post

That is actually a pretty good waterfall, Michael.  Do you have an ETC as well?

Jerry--for us waterfall younglings, can you explain why?

 

Not Jerry but... the 'mountains' are pretty smooth showing a fairly flat FR and the decay is nice and tight at, mostly 120ms or so - and very even too. There is a tiny little bit of ringing at about 30Hz but I would be very happy with that indeed.  How did I do, AJ? 

 

Edit: virgins. We're waterfall virgins. It's been a long time since I could be called a youngling :)

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post #479 of 10744 Old 01-20-2013, 01:38 PM
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Originally Posted by cdnbum88 View Post

I guess now I am getting confused which is easy.

I have the USB mic along with using the HDMI. I am using the laptop and the built in sound card and I use the calibration file that came with the mini dsp email when I ordered the mic. Other than the issues with getting the 8 options as compared to the 2 and changing the speakers from stereo to 5.1, I don't recall having to do any sort of sound card calibration. Am I missing something?

 

No - AIUI you don't need to worry about sound card calibration when using the USB mic and HDMI. It's all in the digital domain (so I am told - thanks AV Mike).

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post #480 of 10744 Old 01-20-2013, 02:15 PM
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Well, I'm not a whole lot further ahead than you are, Stuart, but I'll be glad to share my limited knowledge.

 

When a bass note is struck it will decay over time until it blends with the noise floor of the listening room.  This gradual delay is called ringing or resonance.  The faster the sound decays, i.e. the lower the ringing, the tighter or more well-defined the bass will sound.  A long decay results in bloated, poorly-defined bass.

 

The waterfall measures the rate of decay in the listening room over time.  The vertical axis extends from the noise floor of the listening room, typically around 40dB, to a value high enough to contain the peaks in the response measurement, normally around 90dB.  The horizontal axis shows the frequency response, normally in the range of 40Hz to the upper range of the bass that concerns you, say 100Hz-200Hz.  The third axis represents time, in mille-seconds.

 

Edit:  Based on feedback from Jason, we now agree to sisplay 15-300Hz on the horizontal scale, and to show a 60dB range on the vertical scale (which requires a measurement at a higher level than 75dB).

 

So, looking at Michael's waterfall, we see he has selected 65-95dB on the vertical axis (which really should have a lower value of 40dB), and he is measuring from 20Hz-170Hz.  On the time axis, he has measured 0-300ms. 

 

My understanding is that the objective is to have all bass frequencies decay to below 40dB within the first 300-600ms.  Unfortunately, since Michael's waterfall only goes down to 65dB, he is not showing the noise floor of 40dB.  I retract my earlier statement that the waterfall looks good--we actually don't have enough data.

 

Let's look at some examples (note that my time scale is 0-600ms--we'll come back to that in a moment):

 

First, a vertical axis of 65-95dB;

 

 

Now, 40-95dB:

 

 

And finally, 30-95dB:

 

 

The first waterfall shows that bass frequencies have fully decayed to 65dB within 100-150ms.  This waterfall is meaningless, since we want to show when the decay reaches 40dB, i.e. the noise floor.

 

The second waterfall is useful, because it shows that most, but not all, bass frequencies have decayed below 40dB by 600ms.  The exceptions are at 35Hz, 60Hz and 65Hz, all of which seem to be relatively minor.

 

The third waterfall is not so useful, because it shows decay to 30dB, which is 10dB lower than the noise floor of the room.

 

Now let's see what varying the time axis does.  The graphs above had a 600ms time axis.  Let's go down to 300ms:

 

 

Big difference!  This shows that within 300ms, ALL of the bass frequencies are still present above 40dB.  This doesn't give us much information on where to focus our improvements.  Let's try 450ms now:

 

 

This is showing better information, but there are still quite a few frequencies not fully decayed by 450ms.   To arrive at a meaningful waterfall, we need to continue to increase the time delay until most, or all, of the frequencies are fully decayed.  If this occurs at a time delay of 600ms or lower, we are in reasonable shape.  If it exceeds 600ms, then those frequencies that are not fully decayed at 600ms should be the focus of our improvement effforts.

 

So, what are the take-aways?

 

1.  Always set the lower limit on the vertial axis equal to the noise floor of your listening room (use 40dB if you don't know).

2.  Set the horizontal axis to the frequency range you want to examine, 20Hz-200Hz in my examples.  (Note:  many experts say to ignore the frequencies below 40Hz, because there are very few treatments that can fix resonances in this range.)  Edit:  As mentioned above, we have agreed on a 15-300Hz range for the horizontal axis.

3.  Adjust the time axis, starting at 300ms, until you have a meaningful indicator of where the resonance issues are.

 

Of course, the interesting discussion will be, what value of the time axis represents a "good" decay time, and what values show issues that need to be resolved.  In other words, if everything has decayed in a shorter time than 600ms, is that "good enough"? A second interesting discussion will be, what types of room treatments address issues at specific frequencies, e.g. what to use for a 40Hz resonance vs. a 90 Hz resonance--the answer is likely to be different.

 

Tip:  How do I measure the noise floor of my listening room?  Answer:  In REW, after you have performed the microphone calibration (Step 5 in the Guide), click the red button in the SPL Meter tool.  The meter will display the ambient noise level in the room.  Assuming you have gone to the effort to make sure it is as quiet as possible, the meter will display your room's noise floor.

 

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