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    SubjectRe: ALC883 recording troubles...
    On Thu, Jun 12, 2008 at 11:49 AM, Takashi Iwai <tiwai@suse.de> wrote:
    > At Wed, 11 Jun 2008 20:00:17 +0100,
    > Daniel J Blueman wrote:
    >>
    >> On Tue, Jun 10, 2008 at 6:59 AM, Takashi Iwai <tiwai@suse.de> wrote:
    >> > At Mon, 9 Jun 2008 20:59:00 +0100,
    >> > Daniel J Blueman wrote:
    >> >>
    >> >> Hi Takashi-san,
    >> >>
    >> >> I'm experiencing DC offset with the microphone on 2.6.24 (Ubuntu 8.04
    >> >> LTS x86-64). I can see on Audacity that the DC offset that varies with
    >> >> the recording capture level.
    >> >
    >> > Could you elaborate? The mic bias level could be changed via the pin
    >> > control value. Usually, it's set as VREF 80%.
    >>
    >> When the recording->capture level is set to 0, the mic has no DC
    >> offset as expected. Maxing the recording->capture level, the mic input
    >> is saturated, in between, we see a linear connection.
    >>
    >> >> Plus, the mixer playback->mic-boost
    >> >> muting enables/disables mic-boost in recording.
    >> >
    >> > This is a known bug in alsa-lib mixer abstraction. No kernel issue.
    >>
    >> >> It feels like the ALC883 pins aren't configured quite right. The mobo
    >> >> is an Asus P5E-VM with current BIOS [1]
    >> >>
    >> >> What's the routine to debug this? Would it help to install windows,
    >> >> dump the register space and compare?
    >> >
    >> > You can find *.INI file that contains the default pin configuration
    >> > in Windows. This might be useful in the case BIOS is broken but
    >> > Windows does a black magic.
    >>
    >> That'll be these defaults stashed in the INF file [2]. Let me know if
    >> it's not what you expected and I'll publish the complete INF file.
    >>
    >> > Anyway, please run alsa-info.sh with --no-upload option and show the
    >> > generated file here. It contains the codec information and mixer
    >> > setup.
    >> > http://hg.alsa-project.org/alsa/raw-file/tip/alsa-info.sh
    >>
    >> See [3].
    >>
    >> > Also, you can adjust the pin setting on the fly via hda-verb utility
    >> > below:
    >> > http://ftp.suse.com/pub/people/tiwai/misc/hda-verb-0.2.tar.bz2
    >> >
    >> > Don't forget to build snd-hda-intel module with
    >> > CONFIG_SND_HDA_HWDEP=y to use this command.
    >>
    >> I'll give this a shot if I get time.
    >
    > You can try to adjust VREF value of mic pins.
    > For example, the node 0x18 and 0x19 correspond to the rear and front
    > mics, respectively. Then run the following as root:
    >
    > # ./hda-verb /dev/snd/hwC0D0 0x18 SET_PIN_WID 0x21
    >
    > which will change the widget 0x18 (rear mic) to input-VREF 50%
    > (0x21). The original value is input-VREF 80% (0x24).

    As the mic is working fine, but with this variable DC offset, it felt
    like something needed tweaking in the mixer (summation) node. I
    understand more about the node connectivity now, and found muting the
    front mic mixer input and setting LR gain to 0 at mixer node 23h
    addresses the issue:

    (from page 42 at ftp://66.104.77.130/pc/audio/ALC883_DataSheet_1.3.pdf)

    # ./hda-verb /dev/snd/hwC0D0 0x23 SET_AMP_GAIN_MUTE 0x7180

    Vegard - your HD bus enumeration looks similar and I'd bet the vendor
    followed the same Realtek application note, so can you give this a
    shot too? If not, try mixer node 20h.

    My motherboard (Asus P5E-VM HDMI) has front-panel HD-audio (selectable
    as legacy in the BIOS) connectors, but I've never been able to get
    them working, so left the cables disconnected...surely not a board
    design issue, as default pin configuration wouldn't explain the
    offset?

    Thanks,
    Daniel
    --
    Daniel J Blueman


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