[alsa-devel] acceptable noise level for mic boost

[Takashi Iwai]

At Thu, 21 Nov 2013 17:02:19 +0100,
Oleksij Rempel wrote:
> 
> Am 21.11.2013 16:52, schrieb Takashi Iwai:
> > At Thu, 21 Nov 2013 16:49:17 +0100,
> > Oleksij Rempel wrote:
> >>
> >> Am 21.11.2013 16:41, schrieb Takashi Iwai:
> >>> At Thu, 21 Nov 2013 16:35:20 +0100,
> >>> Oleksij Rempel wrote:
> >>>>
> >>>> Hello Takashi,
> >>>>
> >>>> what is acceptable noise level for mic boost?
> >>>> My laptop has three levels of mic boost (+36dB). Level 3 is useless
> >>>> since noise level will be about 0db. With level 1 i get -12dB noise, so
> >>>> there is almost 12dB room for data... but it is not enough for normal
> >>>> speech, which is about 20dB.
> >>>>
> >>>> Are there any ALSA guide for HW designers, which will say some thing
> >>>> like acceptable levels are 90-20dB?
> >>>> There are some Skype and Microsoft prescriptions for certification.
> >>>> For example M$ prescribe 18dB or more for speech to noise ration for
> >>>> build in mics. It sound like good number to start.
> >>>
> >>> We have no concrete guideline.  Ask anyone's common sense :)
> >>> Actually we already disabled the high mic boost on some machines that
> >>> don't make much sense.
> >>
> >> Suddenly no one answered this question on IRC or mailing list. It will
> >> save some time to have some sort of recommendation ;)
> >> This issue is not dramatic for normal use. But with VoIP and automatic
> >> gain control it make no really noise effects.
> >>
> >>>> In my case, i need to remove mic boost completely to guarantee minimum
> >>>> 18dB SpNR. Suddenly i didn't found correct way to do it.
> >>>> I will be thankful for some tip.
> >>>
> >>> You can add a fixup to override the amp cap.  Take a look at
> >>> patch_realtek.c, e.g. alc269_fixup_limit_int_mic_boost().
> >>
> >> I started with this function, but if i set number of steps to 0,
> >> alsamixer will fail and pulseaudio just ignore this pin.
> > 
> > Give it 1, just like the function above does.
> 
> It means i should provide at least 1 level mic boost?

Well, if you want to kill completely, just override the widget caps
and remove the output amp cap bit in a fixup code (in
HDA_FIXUP_ACT_PRE_PROBE, so that it's done before the parser is
called).


Takashi