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