[alsa-devel] via82xx DC offset at -30dB

Takashi Iwai tiwai at suse.de
Wed Oct 31 09:30:27 CET 2007

At Mon, 29 Oct 2007 01:44:34 +0100,
Peter Plessas wrote:
> Dear List,
> having a Compaq Presario notebook in front of me, running Debian testing
> and a 2.6.18-4-686 kernel, i have a strange DC offset when trying to
> record audio via the mic/line input. As the audacity level meters
> suggest, it resides at -30dBFS.
> Audio comes through and gets recorded though, but the offset severely
> limits the headroom of course.
> The sensitivity of the line/mic input seems to be quite high, although i
> have the mic boost setting turned off of course.
> Setting the module option ac97_quirk=yes did not help either.
> Can it be that a soundcard of this strange behavior is manufactured, or
> is it an alsa/driver issue? I really don't want to install another M$
> operating system to check if it works there, so any help is deeply
> appreciated.
> lspci lists the device as:
> 00:07.5 Multimedia audio controller: VIA Technologies, Inc. VT82C686
> AC97 Audio Controller (rev 20)

AFAIK, there is no specific issue about recording (capture) in via82xx
driver.  So, it should be likely about AC97 codec, if it really

The first thing is to show your mixer setting.  Run "alsactl -f
somefile store" and the file contains the mixer status.  You can show
here together with the contents of /proc/asound/card0/codec97#0/*

Also, trying another apps, such as, arecord is a good test.  In
addition, it's worth to upgrade the ALSA driver version, too.


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