[LAU] ALSA - JACK via loopback device

[Sebastian Rose]

Hello,

currently I have set up a ALSA <-> JACK connection with the loopback 
device approach as described here:
http://www.penguinproducer.com/2011/11/jack-alsa-bridge-kit/

This works fine, except for one problem: Simultaneous playback of 
multiple applications using the ALSA loopback device to channel the 
audiostream to JACK fails with this error:
Device or resource busy

The setup in my asound.conf is quite simple:

# Audio _to_ JACK
pcm.jack_playback {
     type plug
     slave.pcm "hw:Loopback,0,0"
}
# Audio _from_ JACK
pcm.jack_capture {
     type plug
     slave.pcm "hw:Loopback,0,1"
}
pcm.playback_loop {
     type plug
     slave.pcm "hw:Loopback,1,0"
}
pcm.capture_loop {
     type plug
     slave.pcm "hw:Loopback,1,1"
}
pcm.jack_audio {
     type asym
     playback.pcm "jack_playback"
     capture.pcm "jack_capture"
}

I thought that "type plug" should autoconfigure the device in use 
accordingly. I tried to make a manual configuration with dmix but it 
didn't work and I'm not sure if it is necessary. The alsa documentation 
states that dmix is used when the device has no hardware mixer and I'm 
quite sure that a virtual loopback device has none.

best,
semkath