[pulseaudio-discuss] Setting gain when plugging headphone on (non-simple) ALSA controls

[Raymond Yau]

>
> I have a problem of hearing white-noise on my headphones when I plug them
in my laptop. I know the work around:
>
> $ amixer -c 0 cset 'numid=10' 1
> numid=10,iface=MIXER,name='Headphone Mic Boost Volume'
>   ; type=INTEGER,access=rw---R--,values=2,min=0,max=3,step=0
>   : values=1,1
>   | dBscale-min=0.00dB,step=10.00dB,mute=0
>
> OR
>
> $ amixer -c0 sset 'Headphone Mic Boost' 1
> Simple mixer control 'Headphone Mic Boost',0
>   Capabilities: volume
>   Playback channels: Front Left - Front Right
>   Capture channels: Front Left - Front Right
>   Limits: 0 - 3
>   Front Left: 1 [33%] [10.00dB]
>   Front Right: 1 [33%] [10.00dB]
>
> Done, no more white noise. It's all well, but the settings are not
remembered; every time pulseaudio restarts (when I login to my Desktop,
basically):
>
> $ amixer -c 0 cget 'numid=10'
> numid=10,iface=MIXER,name='Headphone Mic Boost Volume'
>   ; type=INTEGER,access=rw---R--,values=2,min=0,max=3,step=0
>   : values=0,0
>   | dBscale-min=0.00dB,step=10.00dB,mute=0
>
> Notice the 0,0? And the white noise is back.
>
> So my end goal is to find my way into hacking pulseaudio so that this is
taken care of without having to do it myself via command line everytime I
use my headphones.
>
> That's where my understanding of things starts to break down. Basically,
I think it's not possible to control this property in pulseaudio at the
moment, so I may need to write/update a module (frankly I'm not actually
sure of that - but I'm not afraid of coding C). I started reading the
coding page on the pulseaudio modules of freedesktop.org, but that did not
really inspire me to find a solution to my issue. So I would like to know
if one of you could guide me a bit.

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/commit/sound/pci/hda/hda_generic.c?id=e7fdd52779a6c2b49d457f452296a77c8cffef6a

You need to mute loopback mixing path,  the noise seem to be feedback of
the combo jack
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