Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 251 - AVS Forum | Home Theater Discussions And Reviews
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post #7501 of 28213 Old 12-22-2013, 09:09 AM
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Originally Posted by jim19611961 View Post

Are you measuring one speaker at a time?

I'm sorry, I really thought this would be simple!

Two speakers (stereo), rotated one at a time a little at a time to see if there would be any difference depending on how they face the MLP. I was surprised that the difference was so dramatic.


Did you really need to quote that entire post in your reply?
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post #7502 of 28213 Old 12-22-2013, 09:11 AM
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Originally Posted by LastButNotLeast View Post

I'm sorry, I really thought this would be simple!
Two speakers (stereo), rotated one at a time a little at a time to see if there would be any difference depending on how they face the MLP. I was surprised that the difference was so dramatic.

If you were measuring both speakers driven at once, your data is flawed due to cancellation (I thought this to be the case by looking at your data).

It is simple. But there are reasons certain measurements have to be taken in a certain way.

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post #7503 of 28213 Old 12-22-2013, 09:15 AM
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Originally Posted by markus767 View Post

^
I'm aiming for around 0.2-0.4s. Generally the focus should be on lower frequencies.

I assume your speaking of RT60 targets?

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post #7504 of 28213 Old 12-22-2013, 09:23 AM
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^
Yes. Of course one has to look at much more data but it's a start.

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post #7505 of 28213 Old 12-22-2013, 09:27 AM
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Originally Posted by markus767 View Post


Already moving on? Did you find out what was causing the erroneous regardings you've got yesterday?
There's something wrong with your measuring setup.

No, I am not moving on, I just don't know what the next step is. You asked if I had verified that the computer is sending a -20dB FS signal to the AVR. I selected -20dB FS in REW, so I assume the signal is the correct level, but don't know how to verify. I am reasonably confidant that my speakers are set by Audyssey Pro to be very close to 75dB, which seems to be confirmed by the REW SPL measurement I posted.

So, I am either mis-interpreting the RTA, or as you say, something else is set up improperly. However, I followed your setup values, so where should I be looking? This conversation started out to provide HTPCat with guidelines on how to set his speakers to 80dB, and I fear we have not done that.
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post #7506 of 28213 Old 12-22-2013, 09:31 AM
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^
Send band-limited pink noise from REW's Generator and measure with your hand-held SPL meter at the listening position. What does it read?


Markus

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post #7507 of 28213 Old 12-22-2013, 09:37 AM
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What are RT60 targets? Do you really consider the decay to 60dB down to be necessary, isn't that kind of a lot for just general purpose HT use?

My decay times above 40Hz are typically under 200ms with the bass traps. 40-20Hz is typically under 300ms. Below 20Hz it is complete rubbish. I was looking at ~40dB decay though I think, that seemed reasonable, but I don't know...

I was asking about decay times because one online calculator (for a well-known panel vendor) apparently uses 400-600ms as the target for HT rooms. They also say RT60 is unattainable in any regular home room. So I don't know what dB decay they are speccing there. What is "enough" to provide good sound?
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post #7508 of 28213 Old 12-22-2013, 09:52 AM
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RT60 should just be used to get you in the ballpark. As a measure it is useful in large room acoustics where the sound field is sufficiently diffuse. The sound field in acoustically small rooms isn't diffuse.

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post #7509 of 28213 Old 12-22-2013, 09:58 AM
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Quote:
Originally Posted by cfraser View Post

What are RT60 targets? Do you really consider the decay to 60dB down to be necessary, isn't that kind of a lot for just general purpose HT use?

My decay times above 40Hz are typically under 200ms with the bass traps. 40-20Hz is typically under 300ms. Below 20Hz it is complete rubbish. I was looking at ~40dB decay though I think, that seemed reasonable, but I don't know...

I was asking about decay times because one online calculator (for a well-known panel vendor) apparently uses 400-600ms as the target for HT rooms. They also say RT60 is unattainable in any regular home room. So I don't know what dB decay they are speccing there. What is "enough" to provide good sound?

There are ongoing and never ending arguments concerning RT60 in small rooms (small rooms are defined as <5000 cu ft in this context or there abouts). I am not going to try and regurgitate them here. Waterfalls and decay plots should tell you all you need to know in this area.

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post #7510 of 28213 Old 12-22-2013, 10:12 AM
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Originally Posted by rhed View Post

Ok.. My mic from cross spectrum is on its way. Still need to get a LT. The problem though is the wifey don't want me to get a PC. She wants me to get a Mac Pro. Now I know the Pro lines have USB ports and a HDMI port. I told her I need a windows base LT to do my work with REW. She's a MAC user. And she said I could run a parallel of OS X or Windows. She showed me on her MAC that she could boot to Windows 7. Friggin amazing. Now question, will using a MAC book with Windows work? If so, I guess I still would down load the Windows REW and the ASIO4ALL drivers?

 

Windows REW may not run under Parallels in the Mac, but it will almost certainly run under Bootcamp. She will know what that means. Either way you will need a copy of Windows 7 to install on the Mac of course.

 

One problem with running Windows on a Mac (either method) is that Windows will run just fine but it may not be able to properly access all peripherals and/or drivers that are required. IDK if this causes any problems with REW. 

 

Although I am a long-time Mac user, I decided to buy a cheap Windows laptop running Windows 7 for my REW work. The support for REW on the Mac is patchy at best and this thread is really a Windows REW thread so you may not be able to get help if you need it. Also, of course, you will be introducing an additional complication which is that you will not be running REW in Windows and not running it in OS-X either. You will be running it in Windows on a Mac. I can see every question you ask being answered with "It may be because you are running REW via Windows on a Mac....". 

 

I also needed a Windows laptop for Audyssey Pro anyway, as it does not have a Mac version - and the same with OmniMic, so I am getting reasonable value from the Windows lappy. 

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post #7511 of 28213 Old 12-22-2013, 11:05 AM
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Of course, Keith is correct--support for Windows is more robust, both here and on the Home Theater Shack REW web site. HST, there are thread participants who have used REW on the MacBook Pro. Look at the note in the very beginning of the Guide, which contains a link to some MacBook guidelines that J_P_A has graciously developed.

Note 2: Thanks to thread contributor J_P_A, a guide on how to use REW with an Apple MacBook Pro has been developed. The solution also uses SoundFlower (A free Inter-application Audio Routing Utility for Mac OS X). The instructions can be viewed here.
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post #7512 of 28213 Old 12-22-2013, 11:12 AM
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Originally Posted by jim19611961 View Post

Waterfalls and decay plots should tell you all you need to know in this area.

Not if you don't know what "good" is. Which is what I was asking a few posts above. Any hints? Thanks.

I guess I just mean for the bass, say in the LFE range. I know my high decays are crap because I can easily hear the reverberation from a hard clap.

[ I am trying to get wall panels from a local maker/vendor (shipping is a killer for these to/in Canada) but don't expect any decent response until "next year". ]
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post #7513 of 28213 Old 12-22-2013, 11:14 AM
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Originally Posted by cfraser View Post

Not if you don't know what "good" is. Which is what I was asking a few posts above. Any hints? Thanks.

I guess I just mean for the bass, say in the LFE range. I know my high decays are crap because I can easily hear the reverberation from a hard clap.

[ I am trying to get wall panels from a local maker/vendor (shipping is a killer for these to/in Canada) but don't expect any decent response until "next year". ]

Post your results. (or link if already posted)

What I meant was, those tools tell more than RT60 for that kind of analysis in a small room.

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post #7514 of 28213 Old 12-22-2013, 11:26 AM
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Originally Posted by cfraser View Post
 
[ I am trying to get wall panels from a local maker/vendor (shipping is a killer for these to/in Canada) but don't expect any decent response until "next year". ]

 

They are really, really easy to make you know. And a fraction of the cost of buying them. If you search on YouTube you'll find dozens of 'how to' videos. Only the most basic of DIY skills are required because all the woodwork etc is covered by the acoustically transparent cloth so you don't need to strive for a cabinetmaker's finish.  I initially bought mine from GIK and they are excellent, but once I realised how easy it is to make them, I made all the rest. Another benefit of making your own is that you are not limited to the standard sizes of 4 feet by 2 feet. If you need a panel that is, say, 6 feet by 2 feet or 5 feet by 3 feet, it's just as easy to make. The pro makers stick to the 4 feet by 2 feet size because that is the standard size of the acoustic absorption material so it makes it easier for them to fabricate the panels, and they have bought in thousands of shipping boxes for that size too. Just a thought.

 

All you need is some timber, cut to size by your hardware store, some screws, some wood glue, the acoustic insulation, acoustically transparent material and a staple gun.

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post #7515 of 28213 Old 12-22-2013, 11:27 AM
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Originally Posted by kbarnes701 View Post

Windows REW may not run under Parallels in the Mac, but it will almost certainly run under Bootcamp. She will know what that means. Either way you will need a copy of Windows 7 to install on the Mac of course.

One problem with running Windows on a Mac (either method) is that Windows will run just fine but it may not be able to properly access all peripherals and/or drivers that are required. IDK if this causes any problems with REW. 

Although I am a long-time Mac user, I decided to buy a cheap Windows laptop running Windows 7 for my REW work. The support for REW on the Mac is patchy at best and this thread is really a Windows REW thread so you may not be able to get help if you need it. Also, of course, you will be introducing an additional complication which is that you will not be running REW in Windows and not running it in OS-X either. You will be running it in Windows on a Mac. I can see every question you ask being answered with "It may be because you are running REW via Windows on a Mac....". 

I also needed a Windows laptop for Audyssey Pro anyway, as it does not have a Mac version - and the same with OmniMic, so I am getting reasonable value from the Windows lappy. 
OK.. Thanks K.. I guess it would be safe to not complicate things. Especially my first time with REW. Windows LT it is then.. One more thing, will REW work with windows 8?
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post #7516 of 28213 Old 12-22-2013, 11:34 AM
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OK.. Thanks K.. I guess it would be safe to not complicate things. Especially my first time with REW. Windows LT it is then.. One more thing, will REW work with windows 8?

Yes.
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post #7517 of 28213 Old 12-22-2013, 11:38 AM
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Quote:
Originally Posted by kbarnes701 View Post

Windows REW may not run under Parallels in the Mac, but it will almost certainly run under Bootcamp. She will know what that means. Either way you will need a copy of Windows 7 to install on the Mac of course.

One problem with running Windows on a Mac (either method) is that Windows will run just fine but it may not be able to properly access all peripherals and/or drivers that are required. IDK if this causes any problems with REW. 

Although I am a long-time Mac user, I decided to buy a cheap Windows laptop running Windows 7 for my REW work. The support for REW on the Mac is patchy at best and this thread is really a Windows REW thread so you may not be able to get help if you need it. Also, of course, you will be introducing an additional complication which is that you will not be running REW in Windows and not running it in OS-X either. You will be running it in Windows on a Mac. I can see every question you ask being answered with "It may be because you are running REW via Windows on a Mac....". 

I also needed a Windows laptop for Audyssey Pro anyway, as it does not have a Mac version - and the same with OmniMic, so I am getting reasonable value from the Windows lappy. 
OK.. Thanks K.. I guess it would be safe to not complicate things. Especially my first time with REW. Windows LT it is then.. 

 

I am all for keeping things simple... I had forgotten that J_P_A had supplied some good Mac/REW info though. Should be worth a look.  Personally, although I'm not a huge fan of Windows, I prefer to use REW under Windows, just because the support in this thread is so much greater. HST, once you have got REW physically working, regardless of the platform it is on, you don't need any further support there. All the remaining support is on how to create and interpret the graphs, and that is platform-independent.

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post #7518 of 28213 Old 12-22-2013, 11:39 AM
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Let me just state a broad opinion.

I think many of us, self included, sometimes are looking for an excuse to quit by looking for litmus tests in all the general categories of measuring criteria. We look at our own data and compare it to these standards. We feel that once we get all of our goals to those standards, we are done.

On the one hand, this is surely a way to find ones room shortcomings and prop them up. It gives us a focal point to concentrate on to steer our energies. Good things come from it and noticeable improvement in sound is often obtained.

But on the other hand, there is no "here is great", "here is good", and "here is terrible" in an absolute sense. The entire spectrum of measurable results are shades of gray. Putting aside subjective preferences which play a major role into the perception of what is great, good and terrible in the first place, no matter where you are on a given measurement, it could be better or further improved.

So at the end of the day, there is no stopping point. There is only the place you choose to stop. "Good enough" could be just that, or it could fall far short of ones potential even within ones constraints.
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Originally Posted by markus767 View Post

^
Send band-limited pink noise from REW's Generator and measure with your hand-held SPL meter at the listening position. What does it read?


Wouldn't it depend on the AVR master volume level? Using the same MV setting as yesterday's mic calibration (-10), the hand-held SPL reads 77-78dB at the MLP.
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Quote:
Originally Posted by cfraser View Post

What are RT60 targets? Do you really consider the decay to 60dB down to be necessary, isn't that kind of a lot for just general purpose HT use?
FWIW, there are international standards for small (less than 3500 cu ft) control rooms and studios: ITU recommends a RT60 of .25s and BBC recommends a RT60 of .3s, both allowing for deviations of ±0.05s from 200Hz to 4kHz; EBU recommends a RT60 of .2s to .4s.

The Mellor/Hedback paper is my go-to for general set-up, with some useful recommendations for decay time:
http://www.acousticfrontiers.com/static/513e1e34e4b00efcff5b05fd/51523db2e4b05218a1268532/51523db3e4b05218a126876f/1340681100537/acoustic_measurement_standards.pdf

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post #7521 of 28213 Old 12-22-2013, 12:06 PM
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Originally Posted by markus767 View Post

But Jerry is sending a -20dB FS RMS signal from within REW. So he should see 85dB (or about 75dB per band) not 77.1dB.
His MV is at -10, so 75 dB is the right target.

BTW, in these cases where REW is being set for a particular ref level, like -20 or -30 dBFS, is the connection to the AVR always digital (HDMI)? If analog, it means nothing, so just want to confirm.

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Not if you don't know what "good" is. Which is what I was asking a few posts above. Any hints? Thanks.

I guess I just mean for the bass, say in the LFE range. I know my high decays are crap because I can easily hear the reverberation from a hard clap.

[ I am trying to get wall panels from a local maker/vendor (shipping is a killer for these to/in Canada) but don't expect any decent response until "next year". ]


Regarding what a "good" waterfall looks like, did you read the waterfall section in the Guide?  I think most of us here agree on some general attributes that indicate a "good" result.

 

For a waterfall graph representing 15-300Hz, using a 450ms window, and a measurement level of at least 40dB above the noise floor, a "good" result is to have all resonances fade below the noise floor level.  In the example below, resonances at 40Hz and 55Hz have not completely decayed, but other frequencies look good (except below 20Hz, where it is extremely difficult to tame resonances).  A waterfall graph would be "excellent" if all resonances were completely decayed below the noise floor in a 300ms window.

 

 

Using the same measurement, the Spectrogram is "good" if all the "flames" stay below 450ms.  In the example below, once again we see small issues at both 40Hz and 55Hz.

 

 

And finally, still using the same measurement, the Decay Graph is "good" if the distance between the 0ms line and the 160ms line exceeds 20dB for the entire 15-300Hz range.

 

 

These are general guidelines only.  Does this help?

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Originally Posted by Roger Dressler View Post


His MV is at -10, so 75 dB is the right target.

BTW, in these cases where REW is being set for a particular ref level, like -20 or -30 dBFS, is the connection to the AVR always digital (HDMI)? If analog, it means nothing, so just want to confirm.

 

Yes, digital using HDMI.

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Quote:
Originally Posted by sdurani View Post


FWIW, there are international standards for small (less than 3500 cu ft) control rooms and studios: ITU recommends a RT60 of .25s and BBC recommends a RT60 of .3s, both allowing for deviations of ±0.05s from 200Hz to 4kHz; EBU recommends a RT60 of .2s to .4s.

The Mellor/Hedback paper is my go-to for general set-up, with some useful recommendations for decay time:
http://www.acousticfrontiers.com/static/513e1e34e4b00efcff5b05fd/51523db2e4b05218a1268532/51523db3e4b05218a126876f/1340681100537/acoustic_measurement_standards.pdf


FWIW, in my 3,000 ft^3 listening room, this is my RT60.  A bit bright, considering the amount of room treatments I have, but probably the open floor plan has something to do with it.  I would prefer to be on the lively side, rather than the dead side.

 

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Quote:
Originally Posted by markus767 View Post

^
Send band-limited pink noise from REW's Generator and measure with your hand-held SPL meter at the listening position. What does it read?


Quote:
Originally Posted by AustinJerry View Post

Wouldn't it depend on the AVR master volume level? Using the same MV setting as yesterday's mic calibration (-10), the hand-held SPL reads 77-78dB at the MLP.
Using MV at -10 and measuring with my RS SPL meter I measured 80dB for each of my 5 speakers. Using -5 MV and FPS of -30 I measured 75dB for each speaker. Do you think I have accomplished what I originally set out to do (changing reference level of 75dB to -5 for MV instead of 0 MV)?

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Originally Posted by Roger Dressler View Post

His MV is at -10, so 75 dB is the right target.

In that case everything you've said is correct.

Markus

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post #7527 of 28213 Old 12-22-2013, 01:49 PM
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Originally Posted by AustinJerry View Post

Wouldn't it depend on the AVR master volume level? Using the same MV setting as yesterday's mic calibration (-10), the hand-held SPL reads 77-78dB at the MLP.

Yes of course it would depend on the master volume. I didn't realize that you had MV set to -10dB. But with that setting your results make perfect sense. Roger already explained why. Case closed?

Markus

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post #7528 of 28213 Old 12-22-2013, 01:56 PM
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Originally Posted by markus767 View Post


Yes of course it would depend on the master volume. I didn't realize that you had MV set to -10dB. But with that setting your results make perfect sense. Roger already explained why. Case closed?

 

Yes, case closed.  Thanks for the advice.  Now I need to incorporate your guidance into the guide, as per Keith's suggestion.

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post #7529 of 28213 Old 12-22-2013, 02:04 PM
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Originally Posted by HTPCat View Post


Using MV at -10 and measuring with my RS SPL meter I measured 80dB for each of my 5 speakers. Using -5 MV and FPS of -30 I measured 75dB for each speaker. Do you think I have accomplished what I originally set out to do (changing reference level of 75dB to -5 for MV instead of 0 MV)?

FPS? If you send band-limited pink noise at -30dB FS RMS to a speaker with your MV at -5dB and you measure 75dB SPL C at the listening position then you've successfully established reference level at -5dB MV.

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post #7530 of 28213 Old 12-22-2013, 02:07 PM
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Yes, case closed.  Thanks for the advice.  Now I need to incorporate your guidance into the guide, as per Keith's suggestion.

Feel free to do so. Let me know if you need further information.

Markus

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