[alsa-devel] [PATCH] ALSA: hda - Implement loopback control switch for Realtek and other codecs

[Takashi Iwai]

On Thu, 10 Dec 2015 08:07:23 +0100,
Raymond Yau wrote:
> 
> 2015-12-09 0:10 GMT+08:00 Takashi Iwai <tiwai at suse.de>:
> 
> > Many codecs, typically found on Realtek codecs, have the analog
> > loopback path merged to the secondary input of the middle of the
> > output paths.  Currently, we don't offer the dynamic switching in such
> > configuration but let each loopback path mute by itself.
> >
> > This should work well in theory, but in reality, we often see that
> > such a dead loopback path causes some background noises even if all
> > the elements get muted.  Such a problem has been fixed by adding the
> > quirk accordingly to disable aamix, and it's the right fix, per se.
> > The only problem is that it's not so trivial to achieve it; user needs
> > to pass a hint string via patch module option or sysfs.
> >
> > This patch gives a bit improvement on the situation: it adds "Loopback
> > Mixing" control element for such codecs like other codecs (e.g. IDT or
> > VIA codecs) with the individual loopback paths.  User can turn on/off
> > the loopback path simply via a mixer app.
> >
> > For keeping the compatibility, the loopback is still enabled on these
> > codecs.  But user can try to turn it off if experiencing a suspicious
> > background or click noise on the fly, then build a static fixup later
> > once after the problem is addressed.
> >
> > Other than the addition of the loopback enable/disablement control,
> > there should be no changes.
> >
> 
> How about the amp in at those mixers of surround jacks / mio jacks ?

An example?


Takashi