Audio input glitches in OS X 10.8
Audio input glitches in OS X 10.8
- Subject: Audio input glitches in OS X 10.8
- From: Edward Waxler <email@hidden>
- Date: Mon, 17 Dec 2012 10:53:33 -0800
- Acceptlanguage: en-US
- Thread-topic: Audio input glitches in OS X 10.8
Until recently, we've had clean audio streaming with our USB devices (1.1 and 2.0) on OS X (from Lion back to Leopard and earlier). After the release of OS X 10.8, glitches could be heard during audio streaming. The glitches are only present in the audio input stream; there are no audible glitches in the output (except, of course, when the output is used for monitoring). They're somewhat intermittent - streaming will be fine for a couple minutes at a time, and then a wave of glitches will come through for about 10 seconds -- after which the audio goes back to normal.
I believe the glitches are introduced AFTER the USB input data is collected. I've tested this using a loopback, where USB input data is copied directly to our USB output buffer, therefore bypassing CoreAudio completely. No glitches were heard on the output in this case, which tells me our USB buffering is working. So the issue must be related to how we're passing data or sending timestamps to CoreAudio.
1) What kind of changes took place in OS X 10.8's version of CoreAudio that would make a USB driver more prone to glitching?
2) Inaccurate timestamps are among the most common causes of glitching during an audio stream. In the past, we could use the HALLab Telemetry window to confirm that it was our timestamps that were wrong. However, the Telemetry window isn't available anymore - I believe this has been reported on these mailing lists in the past. Are there any replacements for it, or other ways to verify/invalidate timestamps or otherwise troubleshoot an audio driver?
Any suggestions would be appreciated.
Thanks in advance,
Ed
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