[alsa-devel] HDA Conexant: is mic boost possible?

Pablo N. Hess phess at linuxnewmedia.com.br
Tue Sep 4 16:14:58 CEST 2007

I have to make the sound chip of a Itautec W7635 (= FIC VA250D) work on 
a Gentoo(-based) distro (I'm now trying Sabayon).
It is a HDA-intel (Conexant codec).

Using my earphones as a stereo mic, recording with 'arecord -f cd' has 
always worked perfectly fine, from alsa-driver-1.0.14 on.

However, when using a regular mono mic (like the ones that come in 
common headsets), recording simply does *not* work.

Here's the quick info:

   playback: ok
     stereo mic: ok
     mono mic: no input at all (very high volume already tried)

   playback: ok (even better than with alsa-driver-1.0.14)
     stereo mic: ok (seems better thatn with alsa-driver-1.0.14)
     mono mic: *very* very low volume, bad quality, lots of low-volume 
noise, too.

Now the paragraphed info:

Playback is perfectly ok since alsa-driver-1.0.14, just like recording 
with an earphone as a stereo mic.

With alsa-driver-1.0.14, definitely no mono-mic input works, no matter 
the settings at alsamixer.
With alsa-driver-1.0.15rc1, mono-mic input works very very bad 
(extremely low volume, terrible quality, lots of clicks and noise).

I guess that the mono mic needs a mic boost in alsa-driver-1.0.15rc1. 
However, with a 'grep -i "mic boost" .../pci/hda/*.c' 
(alsa-driver-1.0.15rc1 source code), it seems that only patch-realtek.c 
and patch-analog.c support this feature.

Is it even possible to add a mic boost feature to this codec?

The output of alsa-info.sh with alsa-driver-1.0.15rc1 is at:

Thanks a lot for any info, and congratulations to all of you for your 
terrific work with ALSA.

Pablo Hess

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