Annoying whitenoise sound coming from snd_hda enabled chipset

[Alexander Motin]

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.

> Now that I'm actually listening to the noise, I'm not sure that it's
> really something
> I would describe as white noise --- the frequency distribution is only
> on a fairly narrow
> band of relatively high frequency.
> Setting the mixer entirely to zero does not eliminate the noise.
> Things like switching between workspaces in KDE or scrolling up and
> down in firefox
> using the scroll wheel cause the noise to disappear during those actions.

CPU or other system activity may influences audio in many aspects, like 
power converters operation modes, CPU/bus/memory/whatever idle power 
management and other. The only recommendation here is not to buy cheap 
components.

> I just now tested switching back to hw.snd.default_unit=0 and using
> the headphone
> jack on the back of the machine (soldered directly to the motherboard), and the
> noise is still present, though slightly quieter than using the front
> panel headphones
> jack.

Depending on configuration, driver could activate additional Headphones 
amplifier on your front connector. It's also usually does not increase 
quality.

PS: The only way to completely avoid system noises is to get good 
external digitally-connected AV-receiver. snd_hda driver now supports 
SPDIF (and I hope HDMI) output and after I have implemented such output 
on my laptop (just soldered one more connector to the existing codec), I 
can say that this the best solution, at least for me. Expensive PCI 
sound cards, like Audugy2 or X-Fi could give comparable quality even via 
analog connectors, but until I anyway have good AV-receiver/amplifier, 
there is no reason for me to use analog connectivity.

-- 
Alexander Motin