Annoying whitenoise sound coming from snd_hda enabled chipset

[Alexander Motin]

Ben Kaduk wrote:
> On Tue, Feb 24, 2009 at 1:31 PM, Alexander Motin <mav at freebsd.org> wrote:
>> Ben Kaduk wrote:
>>> On Sat, Feb 21, 2009 at 12:49 PM, Ben Kaduk <minimarmot at gmail.com> wrote:
>>>> On Sat, Feb 21, 2009 at 8:06 AM, Alexander Motin <mav at freebsd.org> wrote:
>>>>> Garrett Cooper wrote:
>>>>>>   I don't know how else to describe it, but when I turn up my
>>>>>> speakers enough (50%+) and don't have any sound playing, I hear a
>>>>>> whitenoise hiss coming out of them. When I change webpages (nvidia
>>>>>> driver is GIANT locked) or do something else kernel intensive it stops
>>>>>> for a brief second, but apart from that it's an annoying trill sound
>>>>>> almost like a mosquito humming around me waiting to be swatted.
>>>>> I think it may be radio interference with disconnected microphone
>>>>> inputs.
>>>>> Try to set all unneeded mixer volumes to 0, especially mic, monitor,
>>>>> speaker
>>>>> and mix. Inputs often have too sensitive 20-30dB pre-amplifiers. Some
>>>>> codecs
>>>>> have them on all inputs.
>>>> It's hard to be sure, since I'm not sure that I could describe what I
>>>> hear any better than Garret did, but I think I'm seeing the same sort
>>>> of thing on my work desktop.  I'll try setting unneeded volumes to
>>>> zero the next time I'm in, and see if that helps.
>>>>
>>>> dmesg and pciconf are available here:
>>>> http://stuff.mit.edu/afs/sipb.mit.edu/user/kaduk/freebsd/periphrasis/
>>> I'm still getting the noise, even with these mixer settings:
>>> periphrasis# mixer
>>> Mixer vol      is currently set to  25:25
>>> Mixer pcm      is currently set to  25:25
>>> Mixer speaker  is currently set to   0:0
>>> Mixer mix      is currently set to   0:0
>>> Mixer rec      is currently set to   0:0
>>> Mixer monitor  is currently set to   0:0
>>> Recording source:
>> You have set vol and pcm to 25. They are measured not in percents now, there
>> are a logarithmic scales inside codec, so, depending on model, 25 may mean
>> something like -30dB, when you will be able to hear codec's native noise
>> margin, which can quite high cheap codecs and cheap boards.
>>
>> Set your mixer to 80-100 and reduce volume on you speakers/amplifier.
> 
> Sadly, I am using headphones, with no additional amplification.

Then you unlucky. Buy some divider or make it using two jacks and two 
resistors.

Also you may try to disable some in-codec or on-board amplifier if they 
present in your system. First can be controller by setting pin type to 
Line-out instead of Headphones, second sometimes controlled with GPIO 
signals.

> I think I was using the same or similar mixer settings in the old world order,
> with the same loudness at my ear.  I would be surprised if the
> change to logarithmic scale is solely responsible for this noise, but it
> is plausible ...

If you really wish to investigate possible noise source, you can always 
get codec's signal map from it's datasheet or driver output and make 
sure that all unwanted signal sources are blocked. You can get a lot of 
information about driver operation from it's output, especially with 
setting hw.snd.verbose=4. But I does not think you'll find there 
something, driver does this task quite good.

-- 
Alexander Motin