[alsa-devel] Grey noise with HDA Intel PCH

[Takashi Iwai]

At Thu, 14 Aug 2014 12:46:16 +0200,
Julian Wollrath wrote:
> 
> Am Thu, 14 Aug 2014 12:20:11 +0200
> schrieb Clemens Ladisch <clemens at ladisch.de>:
> 
> > Julian Wollrath wrote:
> > > when having my soundcard not muted, I get to hear grey noise over
> > > the speakers or over the headphone
> > >
> > > Simple mixer control 'Master',0
> > >   Mono: Playback 19 [22%] [-51.00dB] [on]
> > 
> > This is rather low.  A lower signal level implies a worse signal-to-
> > noise ratio.
> It is also hearable, with the volume turned up higher and when nothing
> is playing.
> 
> > > Simple mixer control 'Mic',0
> > >   Front Left: Playback 0 [0%] [-34.50dB] [on]
> > >   Front Right: Playback 0 [0%] [-34.50dB] [on]
> > 
> > This plays any noise from the mic input.
> Turning it off makes no difference since capture is turned off anyway:

This is a loopback mixer element, it has nothing to do with capture
stream.

The likely culprit of the static noises is the signal from the analog
loopback.  In some cases, you can disable the whole loopback via
"Loopback Mixing" mixer element on the fly.  In some cases, you'd need
to disable each mixer input (e.g. "Mic Playback Switch").
In some cases (e.g. on some Sony and Dell laptops), you'd need to
disable the complete analog loopback at the initialization.

The last one can be done via the early patching or sysfs
reconfiguration, pass "mixer_nid = 0" hint.  See HD-Audio.txt for a
brief instruction.


Takashi