CoreAudio timing on Mac Pro
CoreAudio timing on Mac Pro
- Subject: CoreAudio timing on Mac Pro
- From: Camille <email@hidden>
- Date: Wed, 27 Dec 2006 01:08:36 +0100
Hello,
I am writing a software that translates MIDI events received from a
virtual endpoint to a FireWire device (using asynchronous commands).
I currently focus on getting the best timing I could, and to do so, I
start with a simple test that is to play quarter notes at 120 bpm in
Logic 7.2.3 and route them to my virtual MIDI input. My application
then passes as fast as it can those events. At 44.1 kHz, two notes
are theoretically spaced by 22050 samples. My application reports
that Logic performs pretty well, and has a jitter of 1 about sample
on a 2,66 GHz Mac Pro and 8 samples on a 1,66 GHz PowerBook.
The problem I have is that the waveform I record with the FireWire
device shows a mean note spacing of 22041 samples, instead of the
expected 22050. If I run the same test with the same version of
Logic on the PowerBook, I get the right result. This test is fully
reproducible.
If I run the same test with Live 5.2 on the Mac Pro, I get the same
discrepancy: 22041 samples ...
I suspect there seem to be a problem with the CoreAudio clock on the
Mac Pro, but as I am not sure at all about that, I'd like to know if
anyone noticed the same problem before.
Thank you in advance for any input!
Best from,
Cam
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