squealing/whistling audio

[Garrett Cooper]

On Tue, Sep 18, 2012 at 10:56 PM, matt <sendtomatt at gmail.com> wrote:
> 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"...

    Could also be a bitmasking/32-bit vs 64-bit bug like what was
fixed last year in snd_emu10kx.
HTH!
-Garrett