[LAU] DC offset

[Rustom Mody]

On Mon, Jan 30, 2012 at 7:29 PM, Fons Adriaensen <fons at linuxaudio.org>wrote:

> On Mon, Jan 30, 2012 at 07:05:38PM +0530, Rustom Mody wrote:
> > On Mon, Jan 30, 2012 at 2:03 PM, Fons Adriaensen <fons at linuxaudio.org
> >wrote:
> >
> > > On Mon, Jan 30, 2012 at 08:41:28AM +0530, Rustom Mody wrote:
> > >
> > > > Immediate context:
> > > > Im trying to capture from firefox using the .asoundrc/jack settings
> shown
> > > > http://jackaudio.org/routing_alsa
> > > > [Track is http://www.raaga.com/play/?id=183659
> > > > I would just buy it if it were for sale; its not. You may have to
> click
> > > > past an ad]
> > >
> > > I just recorded the first minute using the alsa-jack plugin, this
> > > works perfectly and their is no offset in the signal. So it's not
> > > the source or firefox or the plugin.
> > >
> > > > However Ive noticed earlier that when I use my (cheap headset) mike
> to
> > > > record directly into audacity, this similar DC offset occurs. Since
> I am
> > > no
> > > > audio pro I did not know what to google for before seeing the tabs
> in the
> > > > normalize dialog of audacity.
> > >
> > > Could it be that while recording from firefox you had the soundcard
> > > (auto)connected to the same track as well ? That would add the offset
> > > if the cause is your soundcard (which I suspect), even if the headset
> > > is not plugged in.
> > >
> >
> > So you are suggesting I "unconnect" the soundcard (and 'silently'
> record?)
> > Ok how to unconnect the card?
>
> You wrote (see above) that you were using the alsa->jack plugin to record
> from firefox. So you must have connected the track to the outputs of that
> plugin. And I suspect that your recording app has autoconnected itself to
> the soundcard. So you are recording from firefox and the soundcard at the
> same time. Just check this in qjackctl and disconnect the soundcard.
>


Great -- that did it -- almost!
Now one small problem:
firefox appears as rawjack and audacity as portaudio in qjackctl but only
when firefox is playing and audacity is recording.  ie its not enough to
start the apps to be able to rewire as you suggested -- they are not there.
For audacity thats not an issue: I can start the recording and then cut off
the first few seconds.
But for firefox it means I lose the 1st few seconds played.

So I guess I need to figure out how qjackctl chooses its default wirings
and make my chosen ones the default?
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