Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 730 - AVS Forum | Home Theater Discussions And Reviews
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Old 03-16-2017, 03:49 PM
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I was under the impression I could do a sweep of the front right and then the front left and if distance/delay was set correctly or incorrectly I could see this in the 2 phase measurements via a overlay of those 2 sweeps in REW..?

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Old 03-16-2017, 04:15 PM
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Originally Posted by unretarded View Post
I was under the impression I could do a sweep of the front right and then the front left and if distance/delay was set correctly or incorrectly I could see this in the 2 phase measurements via a overlay of those 2 sweeps in REW..?
What is the question?

Did you see the examples in this post?

Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs
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Old 03-16-2017, 04:55 PM
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Hello,
I finally got my miniDSP 2x4 hooked up to 4 PC-2000 subs. I time-aligned the subs using Jerry's guide and ran audyssey pro. I think I finally have a pretty good response for at least the sub region.
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Old 03-16-2017, 05:14 PM
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Originally Posted by MBrown2020 View Post
Hello,
I finally got my miniDSP 2x4 hooked up to 4 PC-2000 subs. I time-aligned the subs using Jerry's guide and ran audyssey pro. I think I finally have a pretty good response for at least the sub region.
Agreed. Look pretty darn good. How about the sound? You happy now?
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Old 03-16-2017, 05:18 PM
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No question from me......it was a reply to the above conversation about measurements of distance and delay etc.

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Old 03-16-2017, 07:05 PM
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Is there a way to determine the absolute distance from the mic to the speaker?
In order for REW to make a determination of the absolute distance to the source (the speaker cone) it would have to 'know' the propagation delay through the entire signal chain:

REW signal > computer sound out latency > to AVR > AVR processor latency > AVR amp > terminals on the driver > sound through the air (temperature, pressure, and humidity dependent) > UMIK > UMIK ADC latency > UMIK USB latency > computer USB latency > OS/driver latency > REW measurement

Sometimes a tape measure works better.
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Old 03-16-2017, 07:39 PM
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Originally Posted by sam_adams View Post
In order for REW to make a determination of the absolute distance to the source (the speaker cone) it would have to 'know' the propagation delay through the entire signal chain:

REW signal > computer sound out latency > to AVR > AVR processor latency > AVR amp > terminals on the driver > sound through the air (temperature, pressure, and humidity dependent) > UMIK > UMIK ADC latency > UMIK USB latency > computer USB latency > OS/driver latency > REW measurement

Sometimes a tape measure works better.
So how do you think Audyssey determines absolute distances? And if Audyssey can do it, why can't REW?

This is really a moot point, because we know that absolute distances are only used to determine relative distances, which in turn are used to calculate delays for time alignment.
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Old 03-16-2017, 11:57 PM
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REW can do it using a physical loopback. Audyssey, or rather the avr, is the same in that it knows the latency in the signal chain in the avr so can conver the measured latency into an accurate physical distance (in the absence of any other delay in the signal chain, e.g. like a AD/DSP/DA in a sub amp)

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Old 03-17-2017, 08:10 AM
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So how do you think Audyssey determines absolute distances? And if Audyssey can do it, why can't REW?
As 3ll3dood mentioned, Audyssey 'knows' the processing delays in the AVR. Now if we could just get an AVR with REW built in...
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Old 03-17-2017, 08:50 AM
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Originally Posted by sam_adams View Post
As 3ll3dood mentioned, Audyssey 'knows' the processing delays in the AVR. Now if we could just get an AVR with REW built in...
Well, the same Audyssey software runs on a bunch of different AVR's, each likely having a different internal processing delay. In order for this to work, the AVR firmware would need to have a parameter that reports to Audyssey what its internal delay is. If Audyssey can retrieve the value from the AVR's memory, then in theory REW could do the same. But this has become an academic discussion...
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Old 03-17-2017, 10:37 AM
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Quote:
Originally Posted by AustinJerry View Post
Well, the same Audyssey software runs on a bunch of different AVR's, each likely having a different internal processing delay. In order for this to work, the AVR firmware would need to have a parameter that reports to Audyssey what its internal delay is. If Audyssey can retrieve the value from the AVR's memory, then in theory REW could do the same. But this has become an academic discussion...
The latency within an AVR is known by Audyssey. The latency in a REW setup is not known by REW.

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Old 03-17-2017, 05:21 PM
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Agreed. Look pretty darn good. How about the sound? You happy now?
Yes the sound is awesome. I ran into a problem using the miniDSP 2x4 unbalanced due to the limit of 7.5ms delay in that I had to kinda fudge the MLP to make it within the limited range.
So I ordered the 2x4 HD which has 80ms delay and will accomodate my setup better, so I predict a little better integration. I noticed the HD also has 2V in and 2V out, (VS .9V in & .9V out) which means that I don't have to worry about clipping the AV8802a, right? The highest voltage i recorded was 1.8V on sub out. So I won't have to worry about the sub trim level right?
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Old 03-17-2017, 05:28 PM
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Originally Posted by MBrown2020 View Post
Yes the sound is awesome. I ran into a problem using the miniDSP 2x4 unbalanced due to the limit of 7.5ms delay in that I had to kinda fudge the MLP to make it within the limited range.
So I ordered the 2x4 HD which has 80ms delay and will accomodate my setup better, so I predict a little better integration. I noticed the HD also has 2V in and 2V out, (VS .9V in & .9V out) which means that I don't have to worry about clipping the AV8802a, right? The highest voltage i recorded was 1.8V on sub out. So I won't have to worry about the sub trim level right?
I think the 2x4 HD will be a better match for your system. The 7.5ms max delay on the regular 2x4 is a real Achilles heel. And no need to worry about the voltages. 2V should be just right--it is what I am using with the balanced 2x4.
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Old 03-17-2017, 05:33 PM
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I think the 2x4 HD will be a better match for your system. The 7.5ms max delay on the regular 2x4 is a real Achilles heel. And no need to worry about the voltages. 2V should be just right--it is what I am using with the balanced 2x4.
Too bad it costs twice as much for that extra couple of ms delays, but we live and learn. Now to sell the old miniDSP
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Old 03-17-2017, 09:40 PM
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Using REW to time-align speakers - feedback requested

Based on recent conversations regarding using REW for time-alignment, I created the attached brief procedure for review. Once the draft has been finalized, I would like to add it ito the REW Guide as a new section. Please review and comment.
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Old 03-17-2017, 10:38 PM
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Looks good to me, my only question is can all this be accomplished over the HDMI or is additional cables required, some sort of loop back ?
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Old 03-18-2017, 12:04 AM
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Originally Posted by AustinJerry View Post
Based on recent conversations regarding using REW for time-alignment, I created the attached brief procedure for review. Once the draft has been finalized, I would like to add it ito the REW Guide as a new section. Please review and comment.
"... but physical measurements are not always as accurate as we might like.". You might want to add why (because processing in devices downstream of the AVR can introduce additional delay).

One doesn't need to specifically find the speaker that is closest first and use that for acoustic timing reference but simply measure them all and then measure distances between the impulse peaks from the leftmost peak (that speaker is "0"). See John's post post 21854.
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Old 03-18-2017, 12:09 AM
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Originally Posted by unretarded View Post
Looks good to me, my only question is can all this be accomplished over the HDMI or is additional cables required, some sort of loop back ?
http://www.roomeqwizard.com/help/hel...ml#acousticref

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Old 03-18-2017, 02:26 AM
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Originally Posted by AustinJerry View Post
Based on recent conversations regarding using REW for time-alignment, I created the attached brief procedure for review. Once the draft has been finalized, I would like to add it ito the REW Guide as a new section. Please review and comment.
Hallo Jerry
Good description. The procedure for the main and surround speakers is clear.
I wonder about the subwoofer, page 7. What criteria do you use to consider when the subwoofer is properly time-aligned? Also, I think that the measurement screen does not show a proper delay for a subwoofer. I have the impression that the measurement screen uses max peak, and not the start of the peak, to calculate the delay.
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Old 03-18-2017, 02:54 AM
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Quote:
Originally Posted by AustinJerry View Post
Based on recent conversations regarding using REW for time-alignment, I created the attached brief procedure for review. Once the draft has been finalized, I would like to add it ito the REW Guide as a new section. Please review and comment.
Hi Jerry
As always many thanks for the help and guidance you give in your excellent guides it is much appreciated.

Page 7 suggests using the same procedure to time align subs
I am slightly confused there seems to be a contradiction as REW suggests

http://www.roomeqwizard.com/help/hel...ml#acousticref

Note that delay values are not accurate for subwoofer measurements due to the limited bandwidth of the subwoofer response, the delay estimate is based on the location of the peak of the impulse response and subwoofers have a broad peak and a delayed response.

Help Index
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Old 03-18-2017, 03:52 AM
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Hallo Jerry
Good description. The procedure for the main and surround speakers is clear.
I wonder about the subwoofer, page 7. What criteria do you use to consider when the subwoofer is properly time-aligned? Also, I think that the measurement screen does not show a proper delay for a subwoofer. I have the impression that the measurement screen uses max peak, and not the start of the peak, to calculate the delay.
Align the beginning of the sub's impulse response to the sat's peak.

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Old 03-18-2017, 04:02 AM
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Align the beginning of the sub's impulse response to the sat's peak.
Hallo Markus,
Thanks for the feedback.
And is the case shown by Jerry properly time aligned? I had the impression that in his example, the "beginning" of the sub impulse is still 2ms after the sat peak.
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Old 03-18-2017, 04:13 AM
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Hallo Markus,
Thanks for the feedback.
And is the case shown by Jerry properly time aligned? I had the impression that in his example, the "beginning" of the sub impulse is still 2ms after the sat peak.
2ms at low frequencies isn't much. Here the user has to play around with sub delay in order to find the best compromise between sub(s) and sats. Aligning the beginning of the sub peak is just a starting point for further optimization.

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I am using old data here and really need to rerun REW but my sub impulse response looks to be inverted?

Appreciate any comments/suggestions
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Old 03-18-2017, 05:58 AM
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Originally Posted by markus767 View Post
"... but physical measurements are not always as accurate as we might like.". You might want to add why (because processing in devices downstream of the AVR can introduce additional delay).

One doesn't need to specifically find the speaker that is closest first and use that for acoustic timing reference but simply measure them all and then measure distances between the impulse peaks from the leftmost peak (that speaker is "0"). See John's post post 21854.
Yes, adding the reason why the physical measurement is not always curate is a good idea. As for identifying the furthest speaker, or the closest speaker, my thinking was that it is sometimes easier for the novice to relate to the fact that the furthest speaker is the one with zero delay, and all closer speakers have a positive delay. I'll see if I can word this section better.

Thanks for your feedback, and the other comments you have provided as well.
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Old 03-18-2017, 06:02 AM
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Originally Posted by turboman123 View Post
Hallo Markus,
Thanks for the feedback.
And is the case shown by Jerry properly time aligned? I had the impression that in his example, the "beginning" of the sub impulse is still 2ms after the sat peak.
I agree that it is more difficult to time align the sub. But, as Markus says, measuring the sub+mains and fine-tuning the distance to produce the smoothest response in the crossover region is typically part of the process as well. Perhaps adding a reminder to do that in this procedure as well would be a good idea. Thanks for pointing this out.
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Old 03-18-2017, 06:03 AM
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Quote:
Originally Posted by Lesmor View Post
I am using old data here and really need to rerun REW but my sub impulse response looks to be inverted?

Appreciate any comments/suggestions
I certainly think it would be worth a try to flip the polarity on the sub channel, and then re-measure. Pick the polarity that produces the smoothest response.
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Old 03-18-2017, 06:17 AM
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Quote:
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I certainly think it would be worth a try to flip the polarity on the sub channel, and then re-measure. Pick the polarity that produces the smoothest response.
Thanks Jerry
I will have to revisit my Dual subwoofer setup as I have one set at 0 and the second at -90 as this gave a far better measured response with multiple different measurements.

But for your impulse guide I would never have been aware of what looks like an inverted impulse.

I will work towards correcting that
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Old 03-18-2017, 06:43 AM
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Quote:
Originally Posted by AustinJerry View Post
As for identifying the furthest speaker, or the closest speaker, my thinking was that it is sometimes easier for the novice to relate to the fact that the furthest speaker is the one with zero delay, and all closer speakers have a positive delay.
I think people would learn more about what relative delay/distance means when using "my" method. And, they would need to measure only once.

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Old 03-18-2017, 06:54 AM
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I think people would learn more about what relative delay/distance means when using "my" method. And, they would need to measure only once.
Not sure why your approach would preclude a second measurement. The purpose of the second measurement is to make sure the entered delays have the desired result. Why would that not still be a good idea?
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