via82xx DC offset at -30dB

via82xx DC offset at -30dB

[Peter Plessas]

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)

regards, PP

PS: please CC: me, as i am not subscribed to alsa-devel (yet)

Re: via82xx DC offset at -30dB

[Takashi Iwai]

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
matters.

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/*
files.

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


Takashi

Re: via82xx DC offset at -30dB

[Peter Plessas]

* Takashi Iwai <tiwai@suse.de> [2007-10-31 11:47]:
> 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
> matters.
> 
> 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/*
> files.
> 
> Also, trying another apps, such as, arecord is a good test.  In
> addition, it's worth to upgrade the ALSA driver version, too.
> 
> 
> Takashio

I just checked with a windows installation, and there the DC is
appearing too. Also with arecord it is the same.
So it might really be the hardware... argh!

alsactl -f file:
http://mona.mur.at/alsactl.txt

cat /proc/asound/card0/codec97#0/:
http://mona.mur.at/ac97_0-0.txt
http://mona.mur.at/ac97_0-0+regs.txt

I might need to get an external soundcard it seems. I wonder how hard it
is to find a working usb stereo card.

Thanks for the help!

Peter