latency - mac clock and the "jiggle"
latency - mac clock and the "jiggle"
- Subject: latency - mac clock and the "jiggle"
- From: Cameron Jones <email@hidden>
- Date: Wed, 20 Nov 2002 09:05:29 -0500
Kevin:
I was intrigued by your email of the 19th about hit scoring and the Mac OS X
clock. I developed a lot of the original Synclavier. software and have a
lot of experience with click tracks, event hits, video frame syncing, etc.
etc. etc.
When I was porting my own application (Synclavier. PowerPC) to OS X I did a
lot of measurements of the underlying time base mechanism of OS X. I was
blown away by the resolution it offers (64-bit counter running at about 25
mhz) as well as how easy it was to use. My goal was to achieve millisecond
accuracy on clicks and event triggers, which I was able to do with a high
priority kernel thread (I have to access PCI hardware every millisecond).
If you are observing sloppy hits, I suspect it would be from how your video
is rendered and not anything to do with the processor (hardware) clock or
its software wrapper.
Are you using house sync? And are you syncing the video with the click
track using SMPTE? If your sequencer follows the time code correctly, it
should easily be able to achieve quarter-frame accuracy (or better) on the
clicks using Core Audio.
I'd be interested to learn the results of any measurements you do on the
timing accuracy of your video rendering. If the video is coming from DVD or
a QuickTime movie, I suspect you will have difficulty finding software that
renders it with precise timing accuracy.
As far as the audio is concerned, I've used CuBase SX running under OS X to
create click tracks that are completely sample-accurate.
Cameron Jones
Salem Technology Associates
--
Cameron W. Jones
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