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

[Michael Trimarchi]

Hi Daniel

On 03/04/13 12:23, Daniel Mack wrote:
> Hi David,
> 
> On 03.04.2013 12:15, David Henningsson wrote:
>> 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.
> 
> There were no relevant changes for snd-usb between the two versions
> mentioned. The only patches that come in mind in this time window are:
> 
>  3e619d041 "USB: EHCI: fix bug in scheduling periodic split transfers"
>  b09a61cc0 "USB: EHCI: fix for leaking isochronous data"

This last one, doesn't give me any problem, just a memory leak and not a choppy
playback (tested on 48Khz, 96Khz, 192Khz 32bit on OMAP3 device) and I don't
think that it can be the reason of the problem.

http://www.m2tech.biz/hiface_dac.html

Michael


> 
> And they have both been back-ported to stable. Copied Alan for reference.
> 
> Any chance some of the bug reporters could try and revert exactly those
> for testing?
> 
> 
> Thanks,
> Daniel
> 
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