[alsa-devel] acceptable noise level for mic boost

[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.

> 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().


Takashi