[alsa-devel] VT1708 clicks & pops

Forest Bond forest at alittletooquiet.net
Tue Sep 20 21:05:34 CEST 2011

Hi Takashi,

Thanks for your response.

On Tue, Sep 20, 2011 at 09:22:23AM +0200, Takashi Iwai wrote:
> At Mon, 19 Sep 2011 19:14:13 -0400,
> Forest Bond wrote:
> > 
> > On Fri, Sep 16, 2011 at 04:36:01PM -0400, Forest Bond wrote:
> > > I have two boards with a VT1708:
> > > 
> > > * VIA EPIA EX15000G
> > > * VIA VB8002
> > > 
> > > I'm using VLC to play audio via PulseAudio to the analog outputs.  The VB8002
> > > sounds great, but the EX15000G has random pops and clicks in the output.  Both
> > > machines are running exactly the same configuration (they are using the same
> > > pre-built OS image).
> > 
> > Maybe this issue would be more approachable if I could produce it without
> > PulseAudio involved?
> Yes.

Heh, I guess I'm probably not going to be able to do that very easily.

> > Incidentally, these boards both produce a crackling/static sound when PulseAudio
> > is playing and the PCM mixer is turned all the way down.  I have seen scattered
> > reports of this in various bug trackers.  The problem does not occur when
> > playing via alsa directly.  One thing I have noticed is that the crackling noise
> > follows the rhythm of the music being played.  It actually sounds like the music
> > has been heavily distorted (i.e. via extreme digital clipping) and then
> > attenuated significantly.
> > 
> > It seems likely that there are driver issues that PulseAudio is exposing.  What
> > can I do to track them down?
> Is the problem related with the driver version?  You mentioned the
> difference of drivers installed on your systems.
> If it's a regression of the driver, it'd be easier to figure out.

No, the issue occurs with both driver versions.

> Other than that, I'd try to adjust PA, e.g. try tsched=0.  Usually
> this kind of problem is because of inaccurate playback position
> reporting from the hardware.  PA relies (too much) on the playback
> position as default.

Using tsched=0 fixes the pops and clicks on the EX15000G.  Any idea why I might
see problems on one board but not the other given how similar they are?

The crackling with PCM volume set to 0 persists with tsched=0.  It seems
unlikely that this isn't driver or hardware issue.  But fixing the pops and
clicks without using tsched=0 is more important to me.  If you can provide
suggestions as to where I might start looking, I would be happy to try and come
up with a fix.

Forest Bond
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