Re: [alsa-devel] Bugs on aspire one A150

[Takashi Iwai]

At Tue, 17 Mar 2009 13:30:12 +0200,
Maxim Levitsky wrote:
> 
> On Tue, 2009-03-17 at 08:57 +0100, Takashi Iwai wrote:
> > At Tue, 17 Mar 2009 02:52:19 +0200,
> > Maxim Levitsky wrote:
> > > 
> > > On Mon, 2009-03-16 at 22:22 +0100, Andreas Mohr wrote:
> > > > Hi,
> > > > 
> > > > On Mon, Mar 16, 2009 at 09:28:39PM +0100, Takashi Iwai wrote:
> > > > > At Mon, 16 Mar 2009 19:06:38 +0100,
> > > > > Andreas Mohr wrote:
> > > > > > I just tried connecting a headset and switching to E-Mic.
> > > > > > What I can say is:
> > > > > > - opposite levels does NOT happen there (E-Mic is "analog micro"-based, right?)
> > > > > > - leaving E-Mic unplugged will actually record from i-Mic (due to properly
> > > > > >   working EAPD mechanism, right?)
> > > > > 
> > > > > The record from mic-jack is via analog path.  The phase-inversion
> > > > > appears only for digital-mic, AFAIK.
> > > > 
> > > > Thought so.
> > > > 
> > > > > > One question still: is this a hardware defect (i.e. could this possibly
> > > > > > be swapped cables of the microphone connector in this model or so?
> > > > > > Not plausible but...), or is this an existing property
> > > > > > of the HDA's dig-mic base? You indicated it's the latter I think...
> > > > > 
> > > > > My guess is that it's a hardware implementation.
> > > > > Maybe for the noise suppression via mic array.
> > > > 
> > > > Not sure what this means.
> > > > 
> > > > > The question is whether the left / right channels recorded from
> > > > > digital mic are really raw data, or they are for modified data
> > > > > (for differential, etc)...  It's hard to guess without the actual
> > > > > data.
> > > > 
> > > > I don't quite follow you here. Is there anything I could do about this?
> > > > 
> > > > Thanks,
> > > > 
> > > > Andreas
> > > 
> > > 
> > > What about exposing the i-mic as a mono only device to userspace?
> > > It is mono after all?
> > 
> > No, it's a mic-array.  And HD-audio cannot handle a mono stream.
> No problem.
> Lets just lie to usespace that it is mono, in kernel driver can pick one
> of channels?

No, the hardware provides only the stereo streams, so the driver,
too.

The downmixing is the job of the user-space.  For example, try the
patch to alsa-lib I sent in my previous post.

> Maybe this is an array, but this doesn't explain the 'quality' of it.
> It is so low (in windows too).

Properly using the mic-array would reduce the noise fairly well.
XP has no mic-array support, IIRC.

Of course, it's possible that Aspire* have badly equipped mic
arrays that don't help much noise suppression...


Takashi
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