[alsa-devel] acceptable noise level for mic boost

Oleksij Rempel linux at rempel-privat.de
Thu Nov 21 16:49:17 CET 2013

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.


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