UMIK-1 timing reference and Phase - Page 6 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #51 of 82 Old 04-02-16, 09:00 AM
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Re: UMIK-1 timing reference and Phase

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A limitation of this initial implementation is that the reference channel is only used for the timing signal, it can't be measured while using it as the timing reference (e.g. if the left channel output is being used for the timing ref, the measurement sweep will only be on the right channel output).
Would you expect a meaningful increase in precision over just measuring that channel without a reference? Put another way, what are the variable latency sources that this feature would eliminate (in the case of measuring the reference channel)?
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post #52 of 82 Old 04-02-16, 02:11 PM
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Re: UMIK-1 timing reference and Phase

Using the timing reference doesn't make any difference to the accuracy of the measurement, the method copes with static latencies. In any case, I have removed the restriction on measuring the ref channel in beta 6, which is now in the usual place.

Changes in beta 6:
  • Added a left/right output channel selector in the Soundcard preferences when using Java drivers, meas sweep only appears on selected channel unless using loopback, when it appears on both
  • When using acoustic timing reference can now also measure the timing ref channel
  • Added an equaliser setting for the Anti-Mode 2.0 Dual Core
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post #53 of 82 Old 04-03-16, 11:21 AM
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Re: UMIK-1 timing reference and Phase

A few more changes for beta 7:
  • Rearranged the input and output selectors on the Soundcard preferences panel
  • Added a "Both" option to the output channel selector when using Java drivers
  • Added output selectors on the measurement dialog
  • Added display of timing reference headroom below the timing ref level control on the measurement dialog
  • Added the timing reference mode and timing reference output name to the measurement Info panel
  • Added a display of the CEA-2010 peak level on the RTA graph
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post #54 of 82 Old 04-03-16, 02:12 PM
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Re: UMIK-1 timing reference and Phase

Although I have not had a chance to try out Beta7 (with output selection on the Measurement dialog) I felt that a 'like' simply did not go far enough.
Many, many thanks John for all the steady improvements to REW - absolutely unbeatable.

Best regards, Mike.
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post #55 of 82 Old 04-15-16, 02:31 PM
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Re: UMIK-1 timing reference and Phase

I will generously assume that other people have already realised an issue with using the new acoustic timing reference - but just in case you have not, I'll try to explain what I have realised.

A proper electrical timing reference will generally allow you to measure the flight time from speaker to microphone. Moving the mic relative to the speaker will show a change in timing due to the distance change - all good, and expected. Moving the mic along an arc, while keeping the speaker distance constant - will show no change in timing, again all good, as expected. Now try the same thing with an acoustic timing reference (using a surround speaker as your reference for example) - if the mic remains stationary the relative timing of various speakers will be accurate - but if you move the mic relative to the reference speaker, all the timings will change - even if you maintained a constant distance to the measurement speakers.

Therefore, if taking single point measurements - acoustic timing works just as well as electrical. But if you plan on taking multiple position samples (that require accurate timing) - don't use acoustic, stay with electrical. It is possible to correct for the reference movement - but it's a bit of a pain. I will grudgingly return to electrical loopback for my next session.

I'm not being critical of John's work - it works as intended, I've used it - just trying to let others know of an inherent issue. That's if others can understand my ramblings

Regards, Mike.
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post #56 of 82 Old 04-15-16, 04:16 PM
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Re: UMIK-1 timing reference and Phase

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Therefore, if taking single point measurements - acoustic timing works just as well as electrical. But if you plan on taking multiple position samples (that require accurate timing) - don't use acoustic, stay with electrical. It is possible to correct for the reference movement - but it's a bit of a pain. I will grudgingly return to electrical loopback for my next session.
Hi Mike,

Are you AV_mike over at AVS? I was asking because you mentioned MSO in an earlier post. Anyway, I thought about this very thing a few weeks ago. At first, I thought it might invalidate MSO results. But then I realized that the acoustic timing reference allows the summation of complex acoustic pressure amplitudes of multiple subs and main speakers taken individually at a given listening position to match what the measurement would be if it were performed with simultaneous excitation. Since each summation of an MSO measurement group normally corresponds to only a single measurement position, the integrity of each summation (the MSO measurement group graph trace) is preserved. If the measurements in a given MSO measurement group were taken at different listening positions, there will be a problem though, and the summation won't be valid. MSO is flexible and allows measurement groups to be defined in this way, but such a summation has no useful physical interpretation that I am aware of.

So it's all good as far as normal usage of MSO is concerned. Normal usage would be the typical scenario for which all the measurements in each MSO measurement group were all taken at the same listening position. Taking phase differences between measurement group summations won't be valid, but I can't see any reason to do that. Also, MSO uses only the magnitude, and not the phase, of the complex summation of the components of a measurement group in its calculations.

Last edited by andyc56; 04-15-16 at 07:56 PM.
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post #57 of 82 Old 04-16-16, 08:09 AM
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Re: UMIK-1 timing reference and Phase

Hi Andyc56,

This is my alter-ego...............................

I must admit, I thought MSO needed the phase to perform the complex summation - as phase and delay share similarities, and would affect how two or more sources interact within the room?

I have been using MSO to combine dissimilar subs - never even got close trying to do it manually - many, many thanks Andy.
I have also been using MSO to get the best sub-sat splice in two listening positions - this is where microphone movement is required. I noticed that my center channel impulse had shifted by over four feet - and yet the center speaker is equi-distant from each listening position. The change was because the mic moved relative to the surround speaker (timing ref source). My initial MSO analysis gave some pretty poor results - until I manually corrected for the impulse timing movement.

While you're here Andy, any changes to MSO on the horizon? I have tried the Target Curve option - but it does not operate as I expected (I'll try to make some notes). A permanently visible RMS error display, and iteration counter would be useful.

Regards Mike (Mike2001, AV_mike)
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post #58 of 82 Old 04-16-16, 11:40 AM
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Re: UMIK-1 timing reference and Phase

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I must admit, I thought MSO needed the phase to perform the complex summation - as phase and delay share similarities, and would affect how two or more sources interact within the room?
Yes, MSO does need the phase to perform the complex summation. However, it does not require that the absolute delay of each measurement be correct. It only requires, for a given complex summation, that the measurements preserve the delays relative to one another of each speaker or sub measured.

This is not unlike how an AVR works internally. An AVR uses zero delay for the most distant speaker to the MLP, then delays closer speakers based on their relative distance to the MLP from the most distant one. So the AVR only uses the relative delays for this calculation. It's a similar idea with MSO.

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I have also been using MSO to get the best sub-sat splice in two listening positions - this is where microphone movement is required. I noticed that my center channel impulse had shifted by over four feet - and yet the center speaker is equi-distant from each listening position. The change was because the mic moved relative to the surround speaker (timing ref source).
If all else is done correctly, this should be okay, as the sub distances should all shift by four feet also, thus preserving the delays relative to one another of each speaker and sub. The latest REW beta allows using a channel under test as the acoustic timing reference, so if this shift in center channel distance bothers you, you can use the center as the timing reference.

Quote:
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My initial MSO analysis gave some pretty poor results - until I manually corrected for the impulse timing movement.
I would absolutely recommend against any second-guessing of REW data by manual time shifting in this way. As long as the measurements were performed correctly, and there's no bug in this new REW feature, REW should take care of all of this internally. In this case, "taking care of it" should manifest itself in a four-foot shift in the impulse responses of the subs at the new position, preserving the relative delays of the subs to one another and to the center channel.

Quote:
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While you're here Andy, any changes to MSO on the horizon? I have tried the Target Curve option - but it does not operate as I expected (I'll try to make some notes). A permanently visible RMS error display, and iteration counter would be useful.
For the time being, I'm not working on it, as I'm dealing with home repairs due to water damage from an unfortunate plumbing incident. I'll add those requests to the list, and I have some other planned improvements too. But they may be a while. I can help you with the target curve in the main MSO thread.
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Last edited by andyc56; 04-16-16 at 12:52 PM.
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post #59 of 82 Old 04-17-16, 09:15 AM
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Re: UMIK-1 timing reference and Phase

Not strictly related to acoustic timing reference, but I have extended the output selection to the signal generator and made a few other changes in beta 8, available in the usual place.
  • Added output selection to the signal generator
  • Added bit length selection to signal generator WAV export (16, 24 or 32-bit WAV files can be generated)
  • Rearranged the signal generator controls
  • Added next and previous 1/3rd octave frequency buttons to the CEA burst generator
  • Added the output name to the measurement Info panel
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post #60 of 82 Old 04-20-16, 01:56 PM
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Re: UMIK-1 timing reference and Phase

I have uploaded beta 9 to the installers directory. This version is earlier than intendede due to an error in the way beta 7 and beta 8 were built. Files made in beta 7 will not open in beta 8 or later and files made in beta 8 will not open in beta 9 or later. The workaround is to open files made in beta 7 or beta 8 in beta 6 or earlier, then save them again. The saved files will open in any later version. There are a couple of small changes in beta 9, long file names should not cause wrapping in the measurement panel and the CEA peak value turns red if any harmonic limits are exceeded. I have removed beta 7 and beta 8.
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