[alsa-devel] VT1708 clicks & pops

[Takashi Iwai]

At Wed, 21 Sep 2011 10:35:10 -0400,
Forest Bond wrote:
> 
> Hi Takashi,
> 
> On Wed, Sep 21, 2011 at 10:39:44AM +0200, Takashi Iwai wrote:
> > At Tue, 20 Sep 2011 15:05:34 -0400, Forest Bond wrote:
> > > 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?
> > 
> > Do they have the same HD-audio controller chip (VIA one)?
> > Usually it's an issue of controller chip, not codec chips, so I wonder
> > if they behave differently even with a same controller.
> 
> I'm not really sure how to identify the controller chip.  alsa-info.sh output is
> here:
> 
> EX15000G:
> http://www.alsa-project.org/db/?f=ea56226a7917391d6adf9078650d3a9395f51b17
> 
> VB8002:
> http://www.alsa-project.org/db/?f=611cc772a3fab7552bbda193b6ad7998f66a60fb
> 
> As I understand it the VT1708 is the codec chip.  Is the audio controller part
> of the south bridge?  Both report having a VT8237.

Yes, and it's VT1708 also meaning a controller chip, apparently.
The controller chip is what PCI ID shows.


> > > The crackling with PCM volume set to 0 persists with tsched=0.
> > 
> > Hrm, which PA version are you using?  I remember vaguely a buggy PA
> > SIMD operations in some old PA versions.
> 
> 1:0.9.22+stable-queue-24-g67d18-0ubuntu3 from Ubuntu Lucid.
> 
> > Also, when you mute the mixer (nor the PA's mixer), e.g. via
> > "alsamixer -c0", the noise goes away, right?
> 
> I do not use the PA mixer.  The noise is present with ALSA's PCM control set to
> zero (-51dB).  If I move the PCM control up one tick (to -50.8dB) the noise goes
> away.

OK, then it's an issue in the sound driver.
Could you give alsa-info.sh outputs both mute-with-noise and without
noise for comparison?


> > > 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.
> > 
> > As mentioned, the usual problem is the inaccurate DMA position
> > reporting, especially when tsched=0 helped.  It means a problem of
> > HD-audio controller.  We have already many workarounds in the driver
> > code, but more investigations are needed in such a case...
> 
> Again, I'm happy to spend the time needed to get this fixed.  If you can provide
> hints on where to look, that would be great.  Can you point me at some git
> commits that fixed similar issues?  I checked the git log but did not find any
> such commits that changed patch_via.c.

Well, there are a few possible causes.  If it's something wrong in the
codec side, it can be a PM code.  The latest driver has a mixer enum
"Dynamic Power-Control".  Try to disable it.

OTOH, if it's in the controller side, where you need to take a look at
is hda_intel.c, or sometimes hda_codec.c.


Takashi