Sound Questions

Hans Fugal hans at fugal.net
Thu Mar 17 15:43:01 MST 2005


First, a little theory lesson.

Many sound cards have only one DAC channel and even more have only one
ADC channel. This is the root of the problem. In UNIX, "everything is a
file" and this device can only be opened by one process at a time.

If your card supports multiple DAC channels, this will either be
transparent to the user or will be separate devices, depending on the
driver. ls /dev/snd and if you have more than one pcmC.D.p file, you are
in luck. If it's not transparent (and obviously it isn't) just set XMMS
to use the non-default ALSA device and it won't get in the way again.

If you aren't so lucky, then the mixing must be done in software
because your sound card is too lazy to do it for you. On Windows this is
built into the OS. On Linux it's not. The options are, in increasing
preferential order, esd, artsd, dmix, and jack if you're really into it.
Jack is by far the best solution technically, but for people not living
and breathing audio it's more hassle than it's worth. I recommend
steering clear of esd and artsd whenever possible, and in general
steering clear of OSS when ALSA is an option. That leaves dmix. Do you
think dmix should be set up out of the box? So do I. dmix for the common
case should be set up with aoss so that all oss applications get dmixed.
Maybe even so that all alsa does too by default. People who care enough
about not having the sound software mixed (there is a quality and
performance issue for sound nuts here) are the ones who care enough to
hack their .asoundrc. Complain to your
distro.

See also this recent thread:
http://music.columbia.edu/pipermail/linux-audio-user/2005-March/021762.html

And these:
http://alsa.opensrc.org/index.php?page=DmixPlugin
http://gentoo-wiki.com/HOWTO_ALSA_sound_mixer_aka_dmix

On Thu, 17 Mar 2005 at 15:05 -0600, Matthew Frederico wrote:
> Something I have noticed with linux, is its sound has weirdness.  For
> example, I am using XMMS, and in order for me to use Skype, I have to
> shut down xmms.  I can't play XMMS and talk via skype at the same
> time.
> 
> using Alsa and I8x0
> 
> I've googled for it, and can't find any answer that can conclusively
> tell me if it can be done or not.
> 
> -- 
> -- Matthew Frederico
> http://www.ultrize.com
> ----------------------------------
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> | This has been a P.L.U.G. mailing. |
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> 

-- 
 .O.  Hans Fugal            | De gustibus non disputandum est.
 ..O  http://hans.fugal.net | Debian, vim, mutt, ruby, text, gpg
 OOO                        | WindowMaker, gaim, UTF-8, RISC, JS Bach
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