Re: squealing/whistling audio

On 09/18/12 23:00, Doug Barton wrote:
> On 9/18/2012 10:56 PM, matt 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.
> Sorry, I should have been more clear. This problem doesn't occur in
> windows, or linux, and last time I checked, didn't occur in freebsd 8. I
> have everything irrlevant zeroed out in mixer.
>
> Doug
>
It was worth a shot. It is possible that each OS (and version) is 
setting the associations up properly though except HEAD on your machine.
Is it a laptop or a desktop board?
Any difference in the nid configuration between freebsd 8 and HEAD?
Does changing any of the hw.snd sysctls (latency, exact rate, vpc_0db) 
have any effect on the sound?

http://freshbsd.org/commit/freebsd/r230551 might be worth a look. I 
couldn't find anything newer that looked like it would have an effect. 
Their are some earlier commits around January that are dealing with 
signal gain that could also have an effect.

Otherwise, I'm not sure where else to look.

Matt