Re: [Alsa-user] Making an (external) soundcard optional

[Dominique M. <dom...@vt...>]

Le Sun, 04 Jan 2009 12:02:44 +0100,
Tobias Gödderz <goe...@un...> a écrit :

> Hi!
> 
> I have a laptop and use an Aureon 5.1 USB card from Terratec at home,
> and my internal sound card if I'm on the road. I am, of course, too lazy
> to switch the default soundcard manually, so I wonder if there is a way
> to either
> 
> i)  make the USB soundcard the default, and automatically use the other
>     if the USB card isn't available
> or
> ii) use a multi device to dupe the audio stream to both cards that
>     doesn't fail if one card isn't available, but silently ignores that
>     and just plays on the other one.
> 
> Of course I could write a script that changes my ~/.asoundrc if the USB
> card is available or not, if there is no sane way to do it with alsa.
> 

It must be also possible to use udev. I am no an expert, but I know that, if
udev load your usb sound card before alsasound, no matter what is
in /etc/modprobe.conf, the usb sound card will be the first one, that imply the
default card.

Most users do not want that and blacklist usb_snd_audio
in /etc/modprobe,d/blacklist.


> At the moment, I have a setup like in ii), but currently it fails if the
> USB card isn't plugged in. My ~/.asoundrc follows.
> 
> pcm.!default plug:both
> 
> ctl.!default {
>    type hw
>    card ICH6
> }
> 
> # This creates a 2-channel interleaved pcm stream based on
> # two 2-channel slave devices.
> 
> pcm.both {
>    type route;
>    slave.pcm {
>        # create a virtual 4-channel device from two sound devices
>        type multi;
>        slaves.a.pcm "intel8x0";
>        slaves.b.pcm "aureon";
>        slaves.a.channels 2;
>        slaves.b.channels 6;
>        bindings.0.slave a;
>        bindings.0.channel 0;
>        bindings.1.slave a;
>        bindings.1.channel 1;
> 
>        bindings.2.slave b;
>        bindings.2.channel 0;
>        bindings.3.slave b;
>        bindings.3.channel 1;
>        bindings.4.slave b;
>        bindings.4.channel 2;
>        bindings.5.slave b;
>        bindings.5.channel 3;
>        bindings.6.slave b;
>        bindings.6.channel 4;
>        bindings.7.slave b;
>        bindings.7.channel 5;
>    }
> 
>    # Map two channels of input to four channels of output
>    ttable.0.0 1;
>    ttable.1.1 1;
> 
>    ttable.0.2 1;
>    ttable.1.3 1;
>    ttable.0.4 1;
>    ttable.1.5 1;
>    ttable.0.6 0.5;
>    ttable.1.6 0.5;
>    ttable.0.7 0.5;
>    ttable.1.7 0.5;
> }
> 
> # Some programs will be unhappy if there is no mixer to talk to,
> # so we set this to one of the cards.
> 
> ctl.both {
>    type hw;
>    card ICH6;
> }
> 
> pcm.aureon {
>     type dmix
>     ipc_key 1024
>     slave {
>         pcm "hw:1"
>         period_time 0
>         period_size 2048
> #        buffer_size 8192
>         buffer_size 65536
>         buffer_time 0
>         periods 128
>         rate 48000
>         channels 6
>      }
>      bindings {
>         0 0
>         1 1
>         2 4
>         3 5
>         4 2
>         5 3
>      }
> }
> 
> pcm.intel8x0 {
>     type dmix
>     ipc_key 2048
>     slave {
>         pcm "hw:0"
>         period_time 0
>         period_size 2048
> #        buffer_size 8192
>         buffer_size 65536
>         buffer_time 0
>         periods 128
>         rate 48000
>         channels 2
>      }
>      bindings {
>         0 0
>         1 1
>      }
> }
> 
> ctl.aureon {
>     type hw
>     card "Audio"
> }
> 
> ctl.intel8x0 {
>     type hw
>     card "ICH6"
> }
> 
> Tobias
>