Re: [Alsa-user] DC Offset on microphone input

[Sergei S. <ste...@li...>]

On Sun, 9 Jan 2011 13:02:39 +0600
IL'dar AKHmetgaleev <akh...@gm...> wrote:

> На Sat, 8 Jan 2011 22:42:30 -0800 (PST)
> Bill Unruh <un...@ph...> записано:
> 
> > On Sun, 9 Jan 2011, IL'dar AKHmetgaleev wrote:
> > 
> > > Greetins.
> > >
> > > I have USB headset which produces a little DC Offset when I'm
> > > recording sound.
> > > Windows magicaly corrects it even inside virtual machine.
> > >
> > > How can I remove DC Offset from my microphone input?
> > 
> > Not sure what you mean. Do you mean that there is an electrical
> > voltage on that input or that when you record, there is a non-zero
> > mean level? If the former, then that is probably to give power to
> > electret condenser microphones to run their fets. If the latter, then
> > you can always apply a digital filter that takes out ultra low
> > frequencies.
> 
> Yes I can apply digital filter if I recording sound. But If I'm using
> headset for VoIP chatting? I'm currently using ladspa plugin in
> asoundrc. But this solution doesn't work with all applications.
> 
> > >
> > > As I know there is a lot cheap hardware which produces DC Offset.
> > 
> > A capacitor removes DC offset. and they are quite cheap.
> 
> Yes. but it's a USB headset. It has USB connector at one side and
> microphone at another side. Hacking and putting capacitor into this
> hardware not very easy solution. 
> 

Why do you think your ADC converts from DC ? I.e. why do you think you
have the DC offset in your recording ?

Regards,
  Sergei.