linux-kernel - Re: ALC883 recording troubles...

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Date:	Thu, 12 Jun 2008 16:23:20 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	"Vegard Nossum" <vegard.nossum@...il.com>
Cc:	"Daniel J Blueman" <daniel.blueman@...il.com>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: ALC883 recording troubles...

At Thu, 12 Jun 2008 16:18:14 +0200,
Vegard Nossum wrote:
> 
> On Thu, Jun 12, 2008 at 4:02 PM, Takashi Iwai <tiwai@...e.de> wrote:
> > At Thu, 12 Jun 2008 15:55:45 +0200,
> > Vegard Nossum wrote:
> >>
> >> On Thu, Jun 12, 2008 at 3:52 PM, Takashi Iwai <tiwai@...e.de> wrote:
> >> > At Thu, 12 Jun 2008 15:48:32 +0200,
> >> > Vegard Nossum wrote:
> >> >>
> >> >> The external mic:
> >> >>
> >> >> Node 0x18 [Pin Complex] wcaps 0x40018f: Stereo Amp-In Amp-Out
> >> >>   Amp-In caps: ofs=0x00, nsteps=0x02, stepsize=0x4f, mute=0
> >> >>   Amp-In vals:  [0x00 0x00]
> >> >
> >> > The input volume is zero.  Try to raise "Mic Boost" (if present)?
> >>
> >> They're already all up.
> >>
> >> Line In Boost = 100
> >> Mic Boost = 100
> >> Internal Mic Boost = 100
> >>
> >> Right after changing all these to max, I've read the value from
> >> card0/codec#0 again:
> >>
> >> Node 0x18 [Pin Complex] wcaps 0x40018f: Stereo Amp-In Amp-Out
> >>   Amp-In caps: ofs=0x00, nsteps=0x02, stepsize=0x4f, mute=0
> >>   Amp-In vals:  [0x00 0x00]
> >>
> >> There doesn't seem to be any difference. Even when changing them all
> >> to 0 in alsamixer, this output stays the same.
> >
> > Weird.  What happens if you execute the verb directly via hda-verb
> > program like below?
> >        hda-verb /dev/snd/hwC0D0 0x18 SET_AMP 0x7002
> >
> 
> Yep, this has the same effect has changing the "Mic Boost" control in
> the Playback section of alsamixer.
> 
> What I discovered now, though, is that I get a much wider range of
> values from the external mic (so playback of the captured data
> actually sounds correct). It actually works, but there is still a very
> strong DC offset that seems dependent on the level of the "Capture"
> control. This offset still makes it unusable for recording, since even
> slightly louder noises will clip the samples.
> 
> It also seems that this control is reset each time I start Audacity
> (even though the "Mic boost" level in alsamixer doesn't change). But I
> guess this unrelated to the DC offset issue.
> 
> Changing the voltage level now (0x21, 0x22, 0x24, with Mic Boost at
> 0x02) doesn't change the DC offset, but has the same effect as before
> (the values fluctuate, but eventually stabilize at the same level).

Hmm, then it's all what I can guess right now.
There might be some vendor-specific settings I don't know of.

To be sure, try the following git tree (master branch), pull on
2.6.26:

    git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6.git

This contains the patches for the next kernel, and some of them are
related with Realtek codecs.


Takashi
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