[pulseaudio-discuss] acceptable noise level for mic boost

[Tanu Kaskinen]

On Fri, 2013-11-29 at 21:56 +0100, Oleksij Rempel wrote:
> Am 29.11.2013 17:22, schrieb Tanu Kaskinen:
> > On Fri, 2013-11-22 at 18:34 +0100, Oleksij Rempel wrote:
> >> Am 22.11.2013 17:48, schrieb Tanu Kaskinen:
> >>> On Thu, 2013-11-21 at 16:42 +0100, Oleksij Rempel wrote:
> >>>> Hello all,
> >>>>
> >>>> i posted this email to ALSA, but probably PA devs have some ideas too.
> >>>>
> >>>> ======================================================================
> >>>> 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.
> >>>>
> >>>> 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.
> >>>>
> >>>> =====================================================================
> >>>>
> >>>> So my question to PA devs. Do pulse audio need to know about noise level
> >>>> of microphone? Will it help to make correct decisions? Especial for VoIP
> >>>> and automatic gain control.
> >>>
> >>> We don't currently have any idea of the noise level, so we don't have
> >>> code for adjusting our decisions based on that information either. So,
> >>> I'd say that pulseaudio doesn't *need* to know about the noise level. Of
> >>> course, if someone someday complains that pulseaudio does bad decisions
> >>> because it doesn't take the noise level into account, then we would need
> >>> that information.
> >>>
> >>
> >> Thank you for your response.
> >> I have more questions:
> >> Skype continuously trying to adjust record level.
> > 
> > I've never used Skype, but I think I've heard that it allows you to
> > disable the automatic gain control. I'd expect that to help with your
> > problem.
> 
> Well, it is workaround but not fix. To make conference call we need
> automatic gain control. Disabling it will work only for single person
> call. The question is how to fix it?
> I tested 7 different notebooks, and 4 of them had this issue. It is
> nearly impossible for alsa to know about all of them.

I don't have a solution. Perhaps it would be better if Skype did AGC in
software instead of modifying the hw amplifier levels? We have
module-echo-cancel in PulseAudio, which includes AGC too, and AFAIK it
does it in software. I know very little about that, though (I don't know
how good it is, and I don't have instructions for setting it up for
Skype).

-- 
Tanu