Issue measuring high latency system - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 9 Old 08-17-16, 12:43 AM Thread Starter
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Issue measuring high latency system

Hi,

My system has a high latency (around 1sec, due to FIR convolution...).

I wonder if it is possible to add an option to delay the stop of the recording playback signal (like in HolmImpulse).

I think this improvement would beneficits few people in the same situation as mine (I can circumver this problem by doing a measurement with the longest measuring signal and to the maximal frequency possible but it is very annoying !).

Thank you very much !
Best regards,
Jean Ibarz
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post #2 of 9 Old 08-17-16, 07:04 AM
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Re: Issue measuring high latency system

The 'Acoustic Timing Reference' is a good option for that situation. The REW help has some info on that feature. It was first introduced Here.
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post #3 of 9 Old 08-17-16, 12:07 PM Thread Starter
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Re: Issue measuring high latency system

Thank you for your answer but I don't think it's not an appropriate solution to my problem : I'm not looking to a solution to be able to get absolute phase timing or anything else related with time measurement. My problem is that REW stops recording when my system is still playing the measure sweep (because the system as a high latency...).

Perhaps I didn't explained very well the problem : is it clearer now ?
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post #4 of 9 Old 08-17-16, 02:56 PM
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Re: Issue measuring high latency system

You haven't understood the solution

The timing reference feature added an option 'Wait for timing reference' which can be used to deal with pretty much any amount of latency.
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post #5 of 9 Old 08-17-16, 03:02 PM Thread Starter
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Re: Issue measuring high latency system

Ok thank you John for the explanation !

So my second problem now is the following : how can I output a reference signal given the fact I use all the (8) outputs of my sound card (and each of them is part of the signal and, for sure, not pure because I do crossover and equalization for each output of my 4-way stereo system) ?

To measure the left/right, I could generate an allpass filter or simulate the delay of the others filters convolved for the crossover and correction, but this seems to me a quite strange solution given this simple problem I am encountering !

PS : I have found a solution : I will make a virtual signal for delay simulation and loopback reference... Hopefully I'm on linux with jackaudio and I can do it digitally

Thank you very much !
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post #6 of 9 Old 08-17-16, 03:13 PM
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Re: Issue measuring high latency system

The timing reference signal only has HF content (5k to 20k), it is generated immediately before the measurement sweep. REW will generate it on any output you select whilst routing the sweep to whichever other (or the same) output you select, so just send it to a speaker that has a tweeter.
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post #7 of 9 Old 08-17-16, 03:24 PM Thread Starter
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Re: Issue measuring high latency system

Thank you so much John !

It seems the version I had (5.14) didn't have the option (wait for timing reference). I updated to the latest beta version and I see this option : I'll do a loopback reference to have an accurate digital delay, and probably an acoustic reference to know how much I need to delay my video playback in VLC to synchronise audio and video signals
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post #8 of 9 Old 08-17-16, 03:38 PM Thread Starter
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Re: Issue measuring high latency system

I cannot check "wait for reference signal" for loopback reference whyyyyy ?
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post #9 of 9 Old 08-18-16, 02:52 PM
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Re: Issue measuring high latency system

The loopback connection carries the same signal as the measurement sweep generated at the same time, so waiting for that to have occurred would mean missing the measurement. Generating it ahead of the measurement sweep would double the measurement time.
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