### 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`	| `20:0`		| none			| MIDI device to connect for input |
| `write`	| `DeviceName`		| none			| MIDI device to connect for output |

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
* `pressure` - Note pressure/aftertouch messages
* `aftertouch` - Channel-wide aftertouch messages
* `pitch` - Channel pitchbend messages

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` and `aftertouch` 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.

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
```
#### Known bugs / problems

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>`.