[alsa-devel] [PATCH -next] ASoC: pandora: Add DAC regulator support

[Grazvydas Ignotas]

On Sun, Feb 7, 2010 at 11:07 AM, Jarkko Nikula <jhnikula at gmail.com> wrote:
> On Sat, 6 Feb 2010 19:33:08 +0200
> Grazvydas Ignotas <notasas at gmail.com> wrote:
>
>> It's on powerdown, there is a faint pop. It appears its the amp (final
>> part in the path), I tried to toggle it while playing /dev/zero
>> manually and it always pops on powerdown. On powerup there is a small
>> sound cutoff too, probably because of amp capacitors charging, but we
>> decided to leave it instead of halting every sound playing program
>> until the amp gets ready.
>>
> My side comment for the /dev/zero test. You may hear pops also
> if /dev/zero is played as unsigned 8-bit samples on signed DAC since
> then samples gets converted to maximum negative value.
>
> So there is a difference how the /dev/zero is played. First command
> below produces a pop because it's playing a pop and second produces a
> pop only if HW is producing it.
>
> aplay /dev/zero
> aplay -f S16_LE /dev/zero

I was testing with '-f cd' which should also be signed. Actually doing
just 'aplay /dev/zero' makes matters worse, there is some additional
'squeek' noise audible when I turn the volume up.

On Mon, Feb 8, 2010 at 1:39 PM, Mark Brown
<broonie at opensource.wolfsonmicro.com> wrote:
> If this goes off too much you might want to tweak the delay ASoC uses to
> defer power down of DAPM widgets after streams stop.  There's a command
> line option pmdown_time, it really ought to have a sysfs file to tweak
> but there's not been any demand.

Yes we are already using that (set to 1 minute), and the sysfs file
would be useful for us (we have a hack for that in our tree).