On May 05 22:30:26, Jacob Meuser wrote:
> On Tue, May 05, 2009 at 09:17:52PM +0200, Jan Stary wrote:
> > On Apr 25 22:23:21, Jacob Meuser wrote:
> > > On Sat, Apr 25, 2009 at 01:15:33PM +0200, Jan Stary wrote:
> > > > Hi all,
> > > >
> > > > I am doing some trivial sound-recording on my Compaq Armada 110 laptop
> > > > (dmesg and mixerctl below). The sound device is
> > > >
> > > > auvia0 at pci0 dev 7 function 5 "VIA VT82C686 AC97" rev 0x20: irq 9
> > > > audio0 at auvia0
> > >
> > > for ac97 devices, the codec is also very important. although the
> > > AD1881A looks pretty standard. no jack sense or anything.
> > >
> > > > and it works without problems.
> > > >
> > > > Now, the laptop has an internal microphone - that tiny little hole
> > > > you have seen on some laptops. It records fine, set up as
> > > >
> > > > inputs.mic=255
> > > > inputs.mic.mute=off
> > > > inputs.mic.preamp=on
> > > > inputs.mic.source=mic0
> > > > record.source=mic
> > > >
> > > > The laptop also has an input for an external mike (the usual small jack,
> > > > just next to the headphones output). When you plug in an external mike,
> > > > the audio chip is smart enough to record from that one, and no longer
> > > > record from the internal mike. (I use Shure SM57 as the external mike,
> > > > which I believe is irrelevant.) Recording with the external mike plugged
> > > > in works fine too, EXCEPT the signal level from the external mike is
> > > > much weaker, and I wonder why.
> > >
> > > maybe there is a separate preamp on the internal mic pin?
> >
> > Well, both mikes do respond to setting
> >
> > inputs.mic.preamp=off/on
> >
> > so I suppose either each has its own preamp,
> > or there is just one mic preamp, pre-amping
> > the one mike (int/ext) that is currently in use.
>
> yes, there is one preamp on the mic pin in the codec.
>
> but, there could be *external to the codec* preamp circuitry between
> the built-in mic and the codec. the codec's datasheet explains how
> to do this.
> > > does changing inputs.mic.source have any effect?
> >
> > inputs.mic.source=mic0 is set by default and behaves as described.
> > inputs.mic.source=mic1 is accepted and results in silence being recorded.
>
> then there is probably jack sense circuitry (again, external to the
> codec), that switches which mic is connected to the mic pin on the
> codec.
That explains it to me, thanks.
Recording works, I just wanted to understand this difference.
Jan
