[gmpi] Re: Reqs 3.9. Time - opening arguments.1

  • From: "Jeff McClintock" <jeffmcc@xxxxxxxxxx>
  • To: <gmpi@xxxxxxxxxxxxx>
  • Date: Sat, 7 Feb 2004 11:13:27 +1300

> Let's do the math and see whether we think this is OK.  At 192 kHz,
> 1ms = 192 samples; over 4 seconds = 48 samples per second of drift;
> recalibrating 4 times per second = max of 12 samples of drift.

To put that in context. My MIDI output clock has a 1ms resolution.  So the
best sync accuracy I need is about 1ms (192 samples).
  Maintaining the UST offset to within 12 samples is overkill. I'm very
comfortable with that accuracy.

 As for syncing to video, at 25 fps, that's one frame every 4ms.  I would
assume an acceptable drift would be anything less than 4ms ( 768 samples ).

In a 'pro' environment, I guess you prefer better than 4ms. That is easily
achievable.

Best Regards,
Jeff

----- Original Message ----- 
From: "Chris Grigg" <gmpi-public@xxxxxxxxxxxxxx>
To: <gmpi@xxxxxxxxxxxxx>
Sent: Saturday, February 07, 2004 9:41 AM
Subject: [gmpi] Re: Reqs 3.9. Time - opening arguments.1


> >  > you can't know UST_per_sample. its not guaranteed constant. both the
> >>  UST timeflow and the audio sample clock have drift.
> >
> >That drift is fairly minimal.  My soundcard sample clock drifts at a rate
of
> >1ms every 4 seconds.  I recalculate 'UST_base_offset' 4 times per second,
> >which is plenty often enough.
>
> Let's do the math and see whether we think this is OK.  At 192 kHz,
> 1ms = 192 samples; over 4 seconds = 48 samples per second of drift;
> recalibrating 4 times per second = max of 12 samples of drift.
>
> -- Chris G.
>
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