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  #1  
Old 12-28-2004, 12:03 AM
jjhuntfox jjhuntfox is offline
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Default Latency Experiments

I've started doing some latency experiments with my 001 / Octopre.

I wanted to see if all ya all... ... think I'm on the right track. Scientifically...

I've started with the click plug on a track. I sent that click signal on a bus and recorded it to another track. I checked for any latency but didn't hear any and didn't see any. I'm a little concerned there might be a little bit of latency in this process even though it is internal. I cant see a way to check the recorded click against the original click.... but it sounds dead on.

My next step has been to record the click output from different sources, monitors and headphones, and compare the latency for each. (Also low latency monitoring on and off...)

I just expand the waveform and see if they line up, vertically. I then use the shift and experiment with different values to get them to line up.

What do you think?

I'll have some detailed results tomorrow, unless you think I'm full o crap.

Thanks,

John
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Old 12-28-2004, 09:17 AM
jjhuntfox jjhuntfox is offline
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Default Re: Latency Experiments

Bump, thought there might be a bit more interest in this....
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Old 12-28-2004, 09:20 AM
Chris Cavell Chris Cavell is offline
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Default Re: Latency Experiments

I have a feeling that the buffer and converter delay compensation that pro tools LE actually does have (it just doesn't have plugin delay compensation) will thwart or confuse your efforts.
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Old 12-28-2004, 09:21 AM
technician technician is offline
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Default Re: Latency Experiments

I'm interested! I'd say still go for it, there are people who will appreciate!
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Old 12-28-2004, 09:38 AM
da BaSsTaRd! da BaSsTaRd! is offline
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Default Re: Latency Experiments

been done already: http://pages.sbcglobal.net/ccash/latency.htm
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Old 12-28-2004, 09:49 AM
Chris Cavell Chris Cavell is offline
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Default Re: Latency Experiments

dB, it would appear that the newer versions of pro tools also compensate for the converter latency in some cases...which has evidently changed since that experiment.
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Old 12-28-2004, 09:56 AM
da BaSsTaRd! da BaSsTaRd! is offline
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Default Re: Latency Experiments

are you sure about that? i think even ADC only compensates for buffer latency. maybe rail knows.
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Old 12-28-2004, 10:07 AM
Chris Cavell Chris Cavell is offline
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Default Re: Latency Experiments

I just checked it, it compensates for the converters in the 002...in most cases...I have found a way to defeat the compensation alltogether, defeating both buffer and converter compensation. I think it won't compensate for any non-digi converters though.
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Old 12-28-2004, 10:16 AM
da BaSsTaRd! da BaSsTaRd! is offline
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Default Re: Latency Experiments

is it giving you problems?
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Old 12-28-2004, 11:04 AM
jjhuntfox jjhuntfox is offline
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Default Re: Latency Experiments

Thanks for the reply's, I'm studying the link that dB posted. Very interesting.

I have some data from yesterday:

Session set up at 44.1K and 24 bit. All sample results are based on 44.1. Obviously a different sample rate will give different results. The HW Buffer is 128. (I am not using a mixer.)

The first test I ran was using my monitor speakers as the sound source. I set up a click track and used various microphones to record it. I ran the mics through my Octopre via lightpipe. I recorded at a normal, about 4 feet, listening distance and then moved the mic right up to the speaker. With all mics the results were about the same. I used a LDC, MDC, SDC and a dynamic mic. Generally all were about 200 samples from 4 feet and 90 samples from right on the tweeter/speaker. (There were some variations in the 4 feet data but that is due to where I held the mic, I was not consistent about 195-220 samples. I mainly wanted to know what it was if I was overdubbing using the studio monitors.)

I then ran the same test but through the 001 mic 1. This time the results were about 175 for 4 feet and 55-57 right on the speaker. Very close to the 51 samples stated in the link dB posted and the slightly higher figure could be the slight delay from the speaker itself of the slight distace from speaker to microphone.

The final test I did was using headphones. One test using the 001 headphone out and one using an external headphone amp fed by outputs 7 + 8. Both were recorded into the 001 mic 1. Both had 57 samples.

I suspect that 90 samples will be the result for that test done through the Octopre. GOing to do that today if I have time.

I ran all the tests with Low Latency on and then again with it off. I saw no difference.

So the 55-57 samples of latency that I found using the 001 inputs is consistent with the article dB posted. The 90 samples of latency with the Octopre and the lightpipe are a little higher. Why, I dunno.

Using speed of sound as 1100 Ft/sec or 1.1 Ft/milisec it takes 3.6 milsec for sound to travel the 4 feet from the speaker or 160 samples... but 160 + 90 is not 200... is my math off? Been a long time since I took physics. Seems more like there is about 45 samples of latency in there and that is close to the 51 samples in dB's article. I'll go measure my listening distance and see if that will clear it up. I bet that will be it cause I just estimated the listening distance.

John

The distance to the speakers was 3 feet making the correct sample / time answer: 2.72 milsec or 120 samples. And that makes sense, at least some sense...
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