latency - mac clock and the "jiggle"
latency - mac clock and the "jiggle"
- Subject: latency - mac clock and the "jiggle"
- From: Kevin Callahan <email@hidden>
- Date: Tue, 19 Nov 2002 10:59:54 -0800
A music student of mine recently enrolled in a scoring class here in
Seattle. The instructor claims the Mac clock is responsible for
drifting and poor syncing of hits. Can someone shed some light on this
vis-a-vis CoreAudio under OSX?
Thanks
Kevin
Here's an email from my student:
===========================
Say you have a cue (a piece of music written for a scene) that is 1
minute
45 seconds long. Based on the scene, you need the orchestra to play
certain things things at precisely 0:31 seconds, 0:55 seconds, 1:15
seconds
and 1:38 second. You go through a set of calculations to determine the
tempo and meter, etc. that will work to reach the +/- accuracy needed
to
get all those hits. The standard is that you can be .1 of a second
early or
.2 of a second late without the audience perceiving any inaccuracy.
Then
you build a click track so you can conduct the orchestra at precisely
the
right tempo, etc.
Apparently the Mac clock is not perfectly consistent and so the click
track
isn't either. Instead it slows and speeds up just slightly, but enough
to
throw the hits outside of the acceptable range. The term he used is
"jiggle". It sounds to me like it's not an OS latency issue but
something
related to the chip.
Partly because of this there a bunch of upper echelon scorers who use
the
Mac for everything but doing the timing calcs and building the click
tracks
and other conducting tools. They instead us a PC-based tool called "The
Oracle". I saw a demo and it is an old-style mid-80's DOS looking UI.
It's
an awful UI but it also has a bunch of other specialized features. The
word
is they won't do a Mac version because of the "jiggle" issue.
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