Re: ALC883 recording troubles...

[Daniel J Blueman]

On Thu, Jun 12, 2008 at 3:23 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> At Thu, 12 Jun 2008 16:18:14 +0200,
> Vegard Nossum wrote:
>>
>> On Thu, Jun 12, 2008 at 4:02 PM, Takashi Iwai <tiwai@xxxxxxx> 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@xxxxxxx> 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.

Maybe. I can readily dump the PCI config space of the Intel HD-audio
controller in Windows and list differences; the datasheet from Intel
allows us to decode the registers. Will this help us any? Of course,
we really need to dump the target behind the HD-bus, but that's
another matter...

> 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
>



-- 
Daniel J Blueman
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