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

  • From: "Jeff McClintock" <jeffmcc@xxxxxxxxxx>
  • To: <gmpi@xxxxxxxxxxxxx>
  • Date: Fri, 6 Feb 2004 09:56:11 +1300

> >I can grok that.  Finally, I grok that.  BuT now I don't see why you need
> >UST per event, if it is linear, it has a defined relationship to the
sample
> >time.
> >
> >UST(sample) = UST_base_offset + sample * UST_per_sample
>
> 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.

If i was super-paranoid, I'd calculate the average drift and extrapolate a
very precise 'UST_base_offset' at any given sampleclock.  However Window's
multimedia timing isn't accurate enough to make it worthwhile.

Don't burden every event with a UST time, the host can provide it (given the
sample time).

Best Regards,
Jeff



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