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

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Message-ID: <19f34abd0806120718g21ddfa3bjbf6f194aa1d3d37d@mail.gmail.com>
Date:	Thu, 12 Jun 2008 16:18:14 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Takashi Iwai" <tiwai@...e.de>
Cc:	"Daniel J Blueman" <daniel.blueman@...il.com>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: ALC883 recording troubles...

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).

Thanks for the help.

Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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