[alsa-devel] [RFC PATCH] Inverted internal mic

[Takashi Iwai]

At Fri, 22 Jun 2012 17:27:51 +0200,
David Henningsson wrote:
> 
> On 06/22/2012 02:46 PM, Takashi Iwai wrote:
> >   /*
> > + * Inverted digital-mic handling
> > + *
> > + * First off, it's a bit tricky.  The "Inverted Internal Mic Capture Switch"
> > + * gives the additional mute only to the right channel of the digital mic
> > + * capture stream.  This is a workaround for avoiding the almost silence
> > + * by summing the stereo stereo stream from some (known to be ForteMedia)
> 
> Stereo stereo? It's "stereo" in stereo! :-)

Yeah, quad channels.  Fixed now.

> > + * digital mic unit.
> > + *
> > + * The logic is to call alc_inv_dmic_sync() after each action (possibly)
> > + * modifying ADC amp.  When the mute flag is set, it mutes the R-channel
> > + * without caching so that the cache can still keep the original value.
> > + * The cached value is then restored when the flag is set off or any other
> > + * than d-mic is used as the current input source.
> 
> Ok, I get it now.
> 
> There is a slight drawback with this (IMO a bit hacky) patch, and that 
> is that you can get a short signal spike on the right channel when you 
> turn "Capture Switch" on while "Inverted Capture" is off. Hopefully it 
> is not a practical problem.

Right, I fully admit it's hacky :)

A good thing by this is, however, that it doesn't touch other parts
too intrusively but just wraps over it.

> Thanks for looking at this long-standing problem :-)

I'm going to commit it once after hearing the test with a real machine
from Eliot.

Thanks for your review!


Takashi