[alsa-devel] acceptable noise level for mic boost

[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.


Takashi