Linux Audio

Linux has two major audio systems: ALSA^ and JACK. Although there is a lot of overlap, ALSA is kind of the lower level system, providing extensive drivers and controls for hardware, and JACK provides a higher level ability to route sound from sources to destinations. Eg. from a mic to a speaker.

To configure JACK, the utility qjackctl is very nice. Be aware, you may need to fully quit and re-launch it to see any changes in setup. The Connections panel allows you to make (and break) connections quickly and temporarily. For more perminant connections use the Patchbay.

Roland Edirol UA-4FX in Linux:

To setup the UA-4FX under ALSA:
https://alsa.opensrc.org/Edirol_UA-4FX The major problem is that the UA-4FX doesn't support computer control of volumn. But ALSA supports a software volumn control:

pcm.!default {
   type             plug
   slave.pcm       "softvol"
}
pcm.softvol {
   type            softvol
   slave {
       pcm         "plughw:UA4FX"
   }
   control {
       name        "SoftMaster"
       card        1
   }
}

note that the web page is wrong, the pcm line in the softvol section should NOT be "pasymed".

Recording from a mono mic leaves one stereo channel with noise on it, so you can put the mono audio on each stereo channel with:

pcm.record_left {
   type        dsnoop
   ipc_key 234884
   slave {
       pcm     "plughw:UA4FX"
       channels 2
   }
   bindings.0  0
}
pcm.record_right {
   type        dsnoop
   ipc_key 2241234
   slave {
       pcm     "plughw:UA4FX"
       channels 2
   }    
   bindings.0  1
} 

To start the JACK server with the UA4FX:
jackd --realtime -d alsa -C hw:UA4FX -P hw:UA4FX &

See also:

• https://alsa.opensrc.org/ Amazing hardware support.
• http://sandsoftwaresound.net/rpi-soft-synth-get-started/

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