[alsa-devel] Asynchronous audio USB chips: choppy playback since 3.8-rc7

[Takashi Iwai]

At Wed, 03 Apr 2013 12:15:25 +0200,
David Henningsson wrote:
> 
> Hi ALSA developers,
> 
> Just to get your attention here on what seems to be an USB audio 
> regression.
> 
> The bug is described in detail here:
> 
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1136110?comments=all
> 
> Quoting the bug:
> 
> "
> This bug seems to affect only a certain kind of hardware, which is 
> called "Asynchronous USB Digital Audio Codec (DAC)". It's said that such 
> a DAC hosts the clock itself (USB Device Host). An ordinary DAC, so 
> called "Synchronous USB DAC", uses the clock hosted by the mother board, 
> which is not affected by this bug.
> 
> When this bug affects an asynchronous USB DAC, the audio played by the 
> DAC is constantly interrupted. The playback itself does not stop, but 
> the output becomes discontinous, filling with constant crackling noises, 
> destroying everything the DAC plays.
> "
> 
> According to the bug reporter, which seems to have done quite a bit of 
> research, this started between 3.8-rc6 and 3.8-rc7 as well as stable 
> kernels and the bug also lists a few commits which could be the cause, 
> none under sound/usb though.

Yes, there is no commits regarding usb-audio itself between 3.8-rc6
and rc7, so the likely culprit is in drivers/usb (usually either
drivers/usb/host or drivers/usb/core).  There are a bunch of changes
there, so further bisection would be appreciated.


Takashi