Re: Choppy Audio Through Core Audio
Re: Choppy Audio Through Core Audio
- Subject: Re: Choppy Audio Through Core Audio
- From: Jeff Moore <email@hidden>
- Date: Mon, 11 May 2009 12:32:54 -0700
Presuming you can get your hands on a system showing the problem, the
first thing I'd do is take a look at what the HAL thinks is going on
using the IO cycle telemetry in HALLab (which you can find in /
Developer/Applications/Audio). The telemetry will give you some idea
about the general reason for the failure:
- if things look normal, then it probably means that there something
going on with how your device and/or driver is using the USB controller.
- If there are errors coming from the kernel trap or bad time stamps,
you will see this in the telemetry data (usually marked in red). The
particular of the symptom will tell you a lot about what's going on.
That said, the only bits of information that are retained about your
device across replugging is the settings of the various controls and
the formats of the streams. Coreaudiod will always attempt to restore
those things to the same state they had prior to unplugging. Apart
from that, the only common element is going to be the device and
whatever you keep around in your driver.
On May 11, 2009, at 8:47 AM, Daniel Rice wrote:
We’re having an issue that we cannot reproduce in house, so I wanted
to bounce it off everyone here to see if I can get any feedback that
may help.
After several hours of leaving the computer running, possibly
sleeping the computer, etc, users report that audio through core
Audio begins to degrade when using our USB Audio device. It becomes
glitchy. The interesting thing to me is that re-plugging the device
does not fix the issue. Only restarting the machine fixes the issue
once it gets into this state.
What, if any information would be stored in Core Audio that could
affect the next replug of our device? Does Core Audio store clock
timing information? Is there any other known reason that Core Audio
behavior would change over time? Our sampleoffsets are fairly
aggressive so I’m wondering if maybe it could have something to do
with that.
Also of interest is that almost every user reporting this is running
an 8-core MacPro. Has anyone seen anything like this?
--
Jeff Moore
Core Audio
Apple
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