[alsa-devel] dmix produces garbled sound on ARM

[Ihar Filipau]

On 6/13/16, Takashi Iwai <tiwai at suse.de> wrote:
> On Mon, 13 Jun 2016 14:32:30 +0200,
> Ihar Filipau wrote:
>>
>> On 6/9/16, Takashi Iwai <tiwai at suse.de> wrote:
>> > On Thu, 09 Jun 2016 16:05:42 +0200,
>> > Ihar Filipau wrote:
>> >>
>> >> The only thing so far I have found is `aplay --dump-hw-params`, but it
>> >> seem to display the allowed ranges, not the defaults/the params which
>> >> are used.
>> >
>> > You just need to check what "aplay -v ..." shows.  For example,
>> > % aplay -Dplug:dmix -v foo.wav
>>
>> I have just retested it with the "aloop", completely without hardware.
>> The garbled sound comes from the software, from the dmix/libasound.
>> The problem is not related to (sound) hardware.
>
> Still it is likely a driver problem.  dmix updates are based on ALSA
> PCM slave timer, i.e. it's synced with PCM period elapses.  That is,
> if the driver updates at a wrong timing, sending the notification
> before the sample data has been processed, you'll get the garbled
> output as you have.
>

But the PCM in the case is the "aloop"? Or not? What other hardware is
involved in the process?

For the sake of a test, I have deactivated the SGTL5000 sound driver,
leaving only the "aloop" as sound device: the result hasn't changed.
But now there is only ALSA software + kernel which are involved.

I have also tried tickless vs fixed HZ kernels (CONFIG_NO_HZ=y vs
CONFIG_HZ_1000=y) but it didn't change anything. The result is the
same.

P.S. I have uploaded the sound file:

http://vocaroo.com/i/s1cU2DRVgJNw

This is supposed to be first 12 seconds of "Annie Lennox - Honestly"
song. (Outside the Germany, it should be readily available on the
YouTube.)