[alsa-devel] Bug#701498: hda: Internal mic does not work on Thinkpad T420s (CX20590 codec)

[David Henningsson]

On 02/24/2013 08:59 PM, Ben Hutchings wrote:
> On Sat, 2013-02-23 at 20:42 +0100, Adrian Lang wrote:
>> Package: src:linux
>> Version: 3.2.35-2
>> Severity: normal
>>
>> There are two microphones in alsamixer and Gnome 3 audio settings (i. e.,
>> pulseaudio), but I can't get any sound using either of them. I think that's the
>> same problem as reported to [openSUSE] and [Ubuntu].
>>
>> The problem persists with 3.7 (3.7.8-1~experimental.1) from
>> experimental.
>>
>> [openSUSE]
>> http://forums.opensuse.org/english/get-technical-help-here/laptop/469210-opensuse-12-1-cannot-get-internal-mic-work-lenovo-g770-laptop.html
>> [Ubuntu]
>> https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/938644

These are different bugs as they concern different hardware.

> I happen to have a Thinkpad T420 with the same audio codec, and the
> internal mic works fine.  (There does seem to be a problem with external
> mics, now that I check, but let's ignore that for now.)  So this is more
> board-specific, not chip-specific, behaviour.

Ok. For the internal mic, this could be the cancelling out problem; see 
the "Inverted Internal Mic" section of this blog post [1] for more 
information.

...as these bugs can sometimes be very specific - when the factory 
finally assembles the laptop, they might select a different component 
just for the DMIC, that has this problem.

-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic

[1] 
http://voices.canonical.com/david.henningsson/2012/05/22/three-audio-bugs-in-12-04/