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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 |
#### 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 multiple channel types
* `cc` - Control Changes
* `note` - Note On/Off messages
* `nrpn` - NRPNs (not yet implemented)
A channel is specified using the syntax `channel<channel>.<type><index>`. The shorthand `ch` may be used instead
of `channel`.
The earlier syntax of `<type><channel>.<index>` is officially deprecated but still supported for compatability
reasons. This support may be removed at some future time.
Channels range from `0` to `15`. Each channel consists of 128 notes (numbered `0` through `127`) and 128 CC's
(numbered likewise), a channel pressure control (also called 'channel aftertouch') and a pitch control.
Each Note also has an additional pressure value associated with it.
Example mappings:
```
midi1.ch0.note9 > midi2.channel1.cc4
midi1.channel15.cc1 > midi1.channel0.note0
```
#### Known bugs / problems
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.
NRPNs are not yet fully implemented, though rudimentary support is in the codebase.
To see which events your MIDI devices output, ALSA provides the `aseqdump` utility. You can
list all incoming events using `aseqdump -p <portname>`.
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