Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 738 - AVS Forum | Home Theater Discussions And Reviews
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post #22111 of 22134 Old Yesterday, 01:46 PM
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Hi guys -

I was making some adjustments to my miniDSP after moving one of my subwoofers and ran into some unexpected results with REW. Here's what I did:

I setup REW with a timing reference (using the center speaker) and ran a frequency sweep
I then ran sweeps with the same center speaker as a timing reference for the front and rear subwoofers, intending to use the delay differences in my miniDSP setup.

Oddly - my initial sweep went wrong somehow: showing a delay of 7.5ms for the center speaker using the center speaker as a timing reference. That obviously doesn't make any sense. Any insight as to why this happened? I re-ran the test with the sweep running from 80Hz to 300hz (eliminating the subs) and ensured my receiver was set to pass the signal directly through.

Thanks,
Mike

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post #22112 of 22134 Old Yesterday, 01:48 PM
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Quote:
Originally Posted by mjmcmahon67 View Post
Hi guys -

I was making some adjustments to my miniDSP after moving one of my subwoofers and ran into some unexpected results with REW. Here's what I did:

I setup REW with a timing reference (using the center speaker) and ran a frequency sweep
I then ran sweeps with the same center speaker as a timing reference for the front and rear subwoofers, intending to use the delay differences in my miniDSP setup.

Oddly - my initial sweep went wrong somehow: showing a delay of 7.5ms for the center speaker using the center speaker as a timing reference. That obviously doesn't make any sense. Any insight as to why this happened? I re-ran the test with the sweep running from 80Hz to 300hz (eliminating the subs) and ensured my receiver was set to pass the signal directly through.

Thanks,
Mike
Post .mdat.

Markus

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post #22113 of 22134 Old Yesterday, 01:56 PM
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I'd dumped the originals, but here's another test with the same issue - speaker 1 1 (Left Front) used as timing reference, yet shows a system delay??

zip file attached
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File Type: zip Timing reference issue.zip (191.6 KB, 18 views)

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post #22114 of 22134 Old Yesterday, 02:21 PM
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OK, what are we looking at here? Hint: label your measurements if you expect feedback.
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post #22115 of 22134 Old Yesterday, 03:30 PM
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Quote:
Originally Posted by AustinJerry View Post
OK, what are we looking at here? Hint: label your measurements if you expect feedback.
Sorry Jerry - I thought I'd explained it thoroughly but obviously not. The first measurement is the reference timing - in this case the Front Left speaker. The second is the subwoofer using the front left as a timing reference. I was following the instructions provided here for measuring time delay - https://www.minidsp.com/applications...ing-time-delay

Under the section "Tabulate your results", it points out that you should have a zero System Delay for the first speaker - which would make sense when you're measuring the same speaker as you use for a time reference. In my case, the system delay showed 6.92ms for a system delay on the same speaker?

I've updated the .zip file with labels to help clarify things.

Thank you,

Mike
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post #22116 of 22134 Old Yesterday, 03:55 PM
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Quote:
Originally Posted by mjmcmahon67 View Post
Sorry Jerry - I thought I'd explained it thoroughly but obviously not. The first measurement is the reference timing - in this case the Front Left speaker. The second is the subwoofer using the front left as a timing reference. I was following the instructions provided here for measuring time delay - https://www.minidsp.com/applications...ing-time-delay

Under the section "Tabulate your results", it points out that you should have a zero System Delay for the first speaker - which would make sense when you're measuring the same speaker as you use for a time reference. In my case, the system delay showed 6.92ms for a system delay on the same speaker?

I've updated the .zip file with labels to help clarify things.

Thank you,

Mike
Thank you for clarifying. Yes, if the Left front is set as the timing reference, and the first measurement is the left front, then these should be a zero delay. What kind of speakers are these?
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post #22117 of 22134 Old Yesterday, 04:08 PM
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Originally Posted by AustinJerry View Post
Thank you for clarifying. Yes, if the Left front is set as the timing reference, and the first measurement is the left front, then these should be a zero delay. What kind of speakers are these?
Jerry -

the mains are B&W 600 series - the reference speaker is a 683S2.

Is there anything I should be adjusting in the REW setup for the timing reference? I ask because I thought I remembered seeing something about 1M Groundplane? The UMIK was placed at the primary listening position.

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post #22118 of 22134 Old Yesterday, 04:18 PM
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Jerry -

the mains are B&W 600 series - the reference speaker is a 683S2.

Is there anything I should be adjusting in the REW setup for the timing reference? I ask because I thought I remembered seeing something about 1M Groundplane? The UMIK was placed at the primary listening position.
I guess I could have looked in your sig...

There are no adjustments required to use the acoustic timing reference. Two recommendations: first, let's see what @markus767 has to say. He is in Europe, so we may not hear his feedback until tomorrow AM. Second, you could open a thread in the REW Forum on HTS titled, "Under what circumstances would a measurement of the speaker set as the timing reference produce a non-zero alignment delay?"
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post #22119 of 22134 Old Yesterday, 04:59 PM
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Thanks Jerry - I'll wait and see what Markus says and engage on HTS if necessary.

I'm also going to step through the 'Getting Started with REW' tutorial again to ensure I get the same results.

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post #22120 of 22134 Old Yesterday, 05:24 PM
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The sweep only goes from 80 Hz to 300 Hz. Do the sweep again from at least 20 Hz for the sub woofer.
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Originally Posted by mjmcmahon67 View Post
Thanks Jerry - I'll wait and see what Markus says and engage on HTS if necessary.

I'm also going to step through the 'Getting Started with REW' tutorial again to ensure I get the same results.
Since I authored that document, I can assure you that there is nothing magic about a measurement with a timing reference.
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post #22122 of 22134 Old Yesterday, 07:56 PM
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Since I authored that document, I can assure you that there is nothing magic about a measurement with a timing reference.
Didn't think that there was - I do know that occasionally things can become corrupted - either thru user configuration or otherwise. I figured starting with a clean slate was a good way to start. Unfortunately, it didn't make any difference.

Hopefully Markus will have some insight!

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post #22123 of 22134 Old Yesterday, 11:23 PM
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Originally Posted by mjmcmahon67 View Post
I'd dumped the originals, but here's another test with the same issue - speaker 1 1 (Left Front) used as timing reference, yet shows a system delay??

zip file attached
You're seeing a difference because you've limited the sweep to 80-300Hz.

Markus

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post #22124 of 22134 Old Today, 05:32 AM
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Originally Posted by markus767 View Post
You're seeing a difference because you've limited the sweep to 80-300Hz.
Doh! Too simple. When the OP tries this, I am sure the delay will be zero as expected. But I believe he is trying to use the impulse to determine sub delays. The sub is typically measured 15-300Hz. Would this mean that the sub impulse measurement will not be accurate as well? Or what should the sub measurement sweep be?
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post #22125 of 22134 Old Today, 05:46 AM
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Originally Posted by AustinJerry View Post
Doh! Too simple. When the OP tries this, I am sure the delay will be zero as expected. But I believe he is trying to use the impulse to determine sub delays. The sub is typically measured 15-300Hz. Would this mean that the sub impulse measurement will not be accurate as well? Or what should the sub measurement sweep be?
Well, the impulse response reflects the frequency response. So it is an accurate representation of that particular frequency range.

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Thanks guys - this is what I was talking about when I talked about "user configuration corruption" - in other words, there was a loose nut behind the keyboard

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Well, the impulse response reflects the frequency response. So it is an accurate representation of that particular frequency range.
So just to make sure I'm on the right track here:

I was attempting to time-align my subs. Using REW and delay settings on my miniDSP, I was attempting to get the delays to match as closely as possible. Am I correct that doing so would time-align the subs?

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post #22128 of 22134 Old Today, 11:04 AM
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Originally Posted by mjmcmahon67 View Post
So just to make sure I'm on the right track here:

I was attempting to time-align my subs. Using REW and delay settings on my miniDSP, I was attempting to get the delays to match as closely as possible. Am I correct that doing so would time-align the subs?
Yes, if you time align your subs you time align your subs Not sure what your question is.
You measure each sub with a common timing reference. Then match the beginning of the impulse peaks or the peaks themselves – whatever you think time-alignment means in an acoustically small space. I would use MSO to come up with adequate delays though.

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Thanks guys -

I relocated the subs and did some more tweaking in REW and miniDSP before running YPAO. This is what the mains + subs frequency response looks like now:



I took a lot of measurements and saved the .mdat to my DropBox (too large for direct attachment) HERE - if anyone has further suggestions for improvement, I'd love to hear them. I played around with the crossover frequency and saw some improvement in the null around 75Hz, but wasn't sure about leaving the mains crossed over at 100Hz.

Thanks again for all the help!

Mike

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post #22130 of 22134 Old Today, 03:39 PM
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Originally Posted by mjmcmahon67 View Post
but wasn't sure about leaving the mains crossed over at 100Hz.
That's my xo. Depends entirely on the system and room, which is why measurements are so important.
You are now entitled to relax for a few minutes and enjoy the results of your efforts.

Michael

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That's my xo. Depends entirely on the system and room, which is why measurements are so important.
You are now entitled to relax for a few minutes and enjoy the results of your efforts.

Michael
LOL - thanks Michael

The question becomes whether to match the Crossover across ALL speakers or just do the FL/FR/C at 100?

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Depends on the other speakers.
Fortunately, I don't have that option, so I don't have that problem.
Guess you're not done, yet.

Michael
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Quote:
Originally Posted by mjmcmahon67 View Post
Thanks guys -

I relocated the subs and did some more tweaking in REW and miniDSP before running YPAO. This is what the mains + subs frequency response looks like now:



I took a lot of measurements and saved the .mdat to my DropBox (too large for direct attachment) HERE - if anyone has further suggestions for improvement, I'd love to hear them. I played around with the crossover frequency and saw some improvement in the null around 75Hz, but wasn't sure about leaving the mains crossed over at 100Hz.

Thanks again for all the help!

Mike
Mike, if you extend the vertical axis enough, anything can look good. The first screenshot below shows a more typical vertical scale and emphasizes a rather aggressive 20dB bass boost. You like bass?

Alignment still seems to be an issue. The next two screenshots show a 2.28ms alignment difference between the two subs, and a 3.17ms alignment difference between the combined sub signal and the left front. The post-YPAO measurement shows an even larger alignment issue between subs and mains.

The alignment between the two subs can be corrected if you have a MiniDSP 2x4. The alignment difference between subs and mains can be fixed using the sub distance tweak.
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post #22134 of 22134 Old Today, 07:14 PM
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Mike, if you extend the vertical axis enough, anything can look good. The first screenshot below shows a more typical vertical scale and emphasizes a rather aggressive 20dB bass boost. You like bass?
CRAP - I left a stupid house curve in place

Quote:
Alignment still seems to be an issue. The next two screenshots show a 2.28ms alignment difference between the two subs, and a 3.17ms alignment difference between the combined sub signal and the left front. The post-YPAO measurement shows an even larger alignment issue between subs and mains.

The alignment between the two subs can be corrected if you have a MiniDSP 2x4. The alignment difference between subs and mains can be fixed using the sub distance tweak.
Okay - this is where I get confused - I thought, particularly based upon Markus' comments earlier today, that matching the system delay values shown in REW would time align the subs. That's clearly not the case as the time aligned subs show a 2.28ms alignment difference. Am I understanding correctly that I should INCREASE the delay on the rear sub by 2.28ms? I'm also unclear on the sub distance tweak and making (intelligent) adjustments in the sub distance and how to align the impulse responses. If you have time and are willing, could we take this to phone?

Thanks,

Mike

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