squealing/whistling audio

[matt]

On 09/18/12 18:01, Doug Barton wrote:
> Sometime in the last couple of months an old problem has resurfaced on
> HEAD, a sort of squealing/whistling sound in the audio, even without
> anything playing. The sound is similar to the wind whistling through
> something.
>
> Before I blindly go off on a bisecting spree, does anyone have a
> suggestion as to where I might look?
>
> Doug
>
>
Electrically that's usually oscillation (too high gain or too much 
electrical feedback) or an unshielded input. My guess would be that 
there is an input that is defined and active in software, but is a 
loose, ungrounded pin in real life. Like a second microphone input on 
the chip, but not actually connected, would be my guess. Can you try 
purging out nids that you don't use with loader tunables (set their as 
to 0)? Or sysctls as reboots aren't as necessary anymore with snd_hda? 
Maybe something changed in software that is seeing inputs that were not 
present. Also just try muting all inputs with mixer...

Just a guess, but when I hear squealing/whistling/howling I think 
"analog" before I think "digital"...

Matt