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The midi backend

The MIDI backend provides read-write access to the MIDI protocol via virtual ports.

Global configuration

Option Example value Default value Description
name MIDIMonster none MIDI client name
detect on off Output channel specifications for any events coming in on configured instances to help with configuration.

Instance configuration

Option Example value Default value Description
read / source 20:0 none MIDI device to connect for input
write / target DeviceName none MIDI device to connect for output
epn-tx short full Configures whether to clear the active parameter number after transmitting an nrpn or rpn parameter

MIDI device names may either be client:port portnames or prefixes of MIDI device names. Run aconnect -i to list input ports and aconnect -o to list output ports.

Each instance also provides a virtual port, so MIDI devices can also be connected with aconnect <sender> <receiver>.

Channel specification

The MIDI backend supports mapping different MIDI events to MIDIMonster channels. The currently supported event types are

  • cc - Control Changes
  • note - Note On/Off messages (also known as note velocity)
  • pressure - Note pressure/aftertouch messages
  • aftertouch - Channel-wide aftertouch messages
  • pitch - Channel pitchbend messages
  • program - Channel program change messages
  • rpn - Registered parameter numbers (14-bit extension)
  • nrpn - Non-registered parameter numbers (14-bit extension)

A MIDIMonster channel is specified using the syntax channel<channel>.<type><index>. The shorthand ch may be used instead of the word channel (Note that channel here refers to the MIDI channel number).

The pitch, aftertouch and program messages/events are channel-wide, thus they can be specified as channel<channel>.<type>.

MIDI channels range from 0 to 15. Each MIDI channel consists of 128 notes (numbered 0 through 127), which additionally each have a pressure control, 128 CC's (numbered likewise), a channel pressure control (also called 'channel aftertouch') and a pitch control which may all be mapped to individual MIDIMonster channels.

Every MIDI channel also provides rpn and nrpn controls, which are implemented on top of the MIDI protocol, using the CC controls 101/100/99/98/38/6. Both control types have 14-bit IDs and 14-bit values.

Example mappings:

midi1.ch0.note9 > midi2.channel1.cc4
midi1.channel15.pressure1 > midi1.channel0.note0
midi1.ch1.aftertouch > midi2.ch2.cc0
midi1.ch0.pitch > midi2.ch1.pitch
midi1.ch0.nrpn900 > midi2.ch0.rpn1
midi2.ch15.note1 > midi1.ch2.program

Known bugs / problems

Extended parameter numbers (EPNs, the rpn and nrpn control types) will also generate events on the controls (CC 101 through 98, 38 and 6) that are used as the lower layer transport. When using EPNs, mapping those controls is probably not useful.

EPN control types support only the full 14-bit transfer encoding, not the shorter variant transmitting only the 7 high-order bits. This may be changed if there is sufficient interest in the functionality.

To access MIDI data, the user running MIDIMonster needs read & write access to the ALSA sequencer. This can usually be done by adding this user to the audio system group.

Currently, no Note Off messages are sent (instead, Note On messages with a velocity of 0 are generated, which amount to the same thing according to the spec). This may be implemented as a configuration option at a later time.

To see which events your MIDI devices output, ALSA provides the aseqdump utility. You can list all incoming events using aseqdump -p <portname>.