Re: [Alsa-user] static when recording from microphone

[Bill U. <un...@ph...>]

Hmm, both the static and the "hum" look very strange. 
The static would look like dropouts except they do not go to 0, but almost
seem as though they are sampling some other waveform. The "hum" has half that
looks like a nice sine wave and half that looks like a decapitated sine wive
-- with a rusty sword.

Sorry, I really have no idea what could be causing this.  Is the same thing
there without the microphone plugged in at all? (or with the microphone inputs
shorted out).
Not sure that either of those would be caused by alsa, although the dropouts
could be I guess. (Have you looked at what happens when you record in stereo
with the alternative channels?)


On Wed, 13 Jul 2011, Brian Pike wrote:

> The "static" is continuous additional noise, which I would describe as a low 
> hum with an additional bouncing crackle.  But I've posted a 300 kilobyte .wav 
> file that I recorded in a quiet room:
>  http://www.unc.edu/~bapike/alsa/hum.wav
> and spectra here (using two different horizontal scales):
>  http: //www.unc.edu/~bapike/alsa/spectrum-log.png
>  http: //www.unc.edu/~bapike/alsa/spectrum-linear.png
> and a zoomed-in picture of the waveform in audacity:
>   http://www.unc.edu/~bapike/alsa/waveform.png
>
> Thanks,
> Brian Pike
>
> On Wed, 13 Jul 2011, Bill Unruh wrote:
>
>>  On Wed, 13 Jul 2011, Brian Pike wrote:
>> 
>> >  Hi,
>> >  I've got a Compaq Presario 12XL505 laptop with a VT82C686 sound chip.
>> >  Playing sound works fine.  However, when I record sound using an 
>> >  external
>> >  microphone, there is static recorded along with the sound. The 
>> >  microphone
>> >  and microphone jack seem to be working fine, since there is no static 
>> >  when
>> >  I have the microphone's input played immediately (i.e., when I change 
>> >  the
>> >  Mic setting in the Playback view of alsamixer).  The microphone also
>> >  sounds fine when used on another computer.
>>
>>  The immediate playback is internal to the sound chip, and has nothing to
>>  do
>>  with what is actually sent to the computer. What kind of static? dropouts?
>>  Additional noise? Can you look at the
>>  recording of the static to see what it looks like? -- large noise spike?
>>  Period of silence? discontinuity? Clipping?
>> 
>> > 
>> >  I've tried recording with different settings and different programs, and 
>> >  I
>> >  even compiled a newer version of alsa-driver (1.0.24) using
>> >  alsa-compile.sh, but the problem remains.  Any suggestions?
>> > 
>> >  By the way, the output of alsa-info.sh (when using the ALSA drivers
>> >  included in Debian's linux-image-2.6.32-5-686 package) is available at
>> >  http://pastebin.com/jSRzJLrW
>> >  Please let me know if you want any other information.
>> > 
>> >  Thanks,
>> >  Brian Pike
>> > 
>> 
>> 
>