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    SubjectRe: [alsa-devel] Bugs on aspire one A150
    At Mon, 16 Mar 2009 18:30:00 +0100,
    Andreas Mohr wrote:
    >
    > Hi,
    >
    > On Mon, Mar 16, 2009 at 06:15:39PM +0100, Takashi Iwai wrote:
    > > At Mon, 16 Mar 2009 18:00:15 +0100,
    > > Andreas Mohr wrote:
    > > >
    > > > Hi,
    > > >
    > > > On Mon, Mar 16, 2009 at 05:19:38PM +0100, Takashi Iwai wrote:
    > > > > At Mon, 16 Mar 2009 17:06:35 +0100,
    > > > > 私 wrote:
    > > > > >
    > > > > > > > What are "sliders"?
    > > > > > >
    > > > > > > Umm, volume level controls.
    > > > > >
    > > > > > Yes but there are many of such :)
    > > > > >
    > > > > > More exactly, from the driver perspective, there are no volume
    > > > > > controls but only there are control elements with integer values.
    > > > > > Do you mean "Capture Volume" control or which one?
    > > >
    > > > Hmm, ok, this needs to be more precise:
    > > > In gamix (codec "HDA Intel : Realtek ALC268"), the Capture Volume control.
    > >
    > > Yeah, that's more understandable :)
    > >
    > > BTW, does "Capture Volume" influence on the recording level even for
    > > the built-in mic, right? I'm asking this because the digital mic on
    > > STAC/IDT codecs isn't controlled via "Capture Volume" control that is
    > > bound to an ADC widget. (That's why "Digital Capture Volume" control
    > > exists. It's a value used by alsa-lib softvol plugin for "default"
    > > PCM.)
    >
    > Yes, Capture Volume does influence i-Mic level.
    > The Digital Capture control, however, doesn't influence level.
    > As doesn't the Mic Boost Capture control (probably about e-Mic only?).

    The "Digital Capture Volume" has effect only when "default" PCM is used.
    If you record via "hw" or "plughw", it's unused.

    > > > > > And, is the behavior consistent regardless of the value high, i.e.
    > > > > > the key is only whether the values for both channels are identical?
    > > > >
    > > > > BTW, what if you record with the following definition?
    > > > > Put the below to ~/.asoundrc
    > > > >
    > > > > pcm.imix {
    > > > > type plug
    > > > > slave.pcm "hw"
    > > > > ttable.0.0 0.5
    > > > > ttable.0.1 -0.5
    > > > > }
    > > > >
    > > > > and record like
    > > > >
    > > > > % aplay -Dimix -c1 foo.wav
    > > >
    > > > Does NOT exhibit the "equal sliders == no sound" bug (apart from this sliders
    > > > are acting normally, i.e. slider low == no sound), despite being a
    > > > "plug" type definition (this is what you wanted to discern, right? ;).
    > >
    > > Interesting. This implies that one channel is inverted indeed.
    >
    > Oh, you mean "inverted" as in "_hardware_ channel which provides opposite
    > sample values as compared to the other channel"?

    Right. My guess is that the hardware provides left (or right) channel
    is multiplied by -1 (yep "inverted" is no correct word choice).

    > > As default the alsa-lib plugin downmixes a stereo stream to a mono
    > > stream simply by left/2 + right/2. The above changes the routing
    > > policy as left/2 - right/2.
    >
    > That exactly matches my current stream of thought (while reading
    > "one channel is inverted" above).
    >
    > > So we need to pass some information to change this kind of thing...
    >
    > That's something specific to ALC268 codec setup, right?
    > ("ALC268 digital mic == left plus right channel, but inverted setup"?)

    No. It's specific to the digital-mic side.


    Takashi


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