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

[Raymond Yau]

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 ?