diff options
Diffstat (limited to 'backends/jack.md')
| -rw-r--r-- | backends/jack.md | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/backends/jack.md b/backends/jack.md new file mode 100644 index 0000000..b6ff5a9 --- /dev/null +++ b/backends/jack.md @@ -0,0 +1,84 @@ +### The `jack` backend + +This backend provides read-write access to the JACK Audio Connection Kit low-latency audio transport server for the +transport of control data via either JACK midi ports or control voltage (CV) inputs and outputs. + +#### Global configuration + +| Option | Example value | Default value | Description | +|---------------|-----------------------|-----------------------|-----------------------| +| `debug` | `on` | `off` | Print `info` level notices from the JACK connection | +| `errors` | `on` | `off` | Print `error` level notices from the JACK connection | + +#### Instance configuration + +| Option | Example value | Default value | Description | +|---------------|-----------------------|-----------------------|-----------------------| +| `name` | `Controller` | `MIDIMonster` | Client name for the JACK connection | +| `server` | `jackserver` | `default` | JACK server identifier to connect to | + +Channels (corresponding to JACK ports) need to be configured with their type and, if applicable, value limits. +To configure a port, specify it in the instance configuration using the following syntax: + +``` +port_name = <type> <direction> min <minimum> max <maximum> +``` + +Port names may be any string except for the instance configuration keywords `name` and `server`. + +The following `type` values are currently supported: + +* `midi`: JACK MIDI port for transmitting MIDI event messages +* `cv`: JACK audio port for transmitting DC offset "control voltage" samples (requires `min`/`max` configuration) + +`direction` may be one of `in` or `out`, as seen from the perspective of the MIDIMonster core, thus +`in` means data is being read from the JACK server and `out` transfers data into the JACK server. + +The following example instance configuration would create a MIDI port sending data into JACK, a control voltage output +sending data between `-1` and `1`, and a control voltage input receiving data with values between `0` and `10`. + +``` +midi_out = midi out +cv_out = cv out min -1 max 1 +cv_in = cv in min 0.0 max 10.0 +``` + +Input CV samples outside the configured range will be clipped. The MIDIMonster will not generate output CV samples +outside of the configured range. + +#### Channel specification + +CV ports are exposed as single MIDIMonster channel and directly map to their normalised values. + +MIDI ports provide subchannels for the various MIDI controls available. Each MIDI port carries +16 MIDI channels (numbered 0 through 15), each of which has 128 note controls (numbered 0 through 127), +corresponding pressure controls for each note, 128 control change (CC) controls (numbered likewise), +one channel wide "aftertouch" control and one channel-wide pitchbend control. + +A MIDI port subchannel 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 following values are recognized for `type`: + +* `cc` - Control Changes +* `note` - Note On/Off messages +* `pressure` - Note pressure/aftertouch messages +* `aftertouch` - Channel-wide aftertouch messages +* `pitch` - Channel pitchbend messages + +The `pitch` and `aftertouch` events are channel-wide, thus they can be specified as `channel<channel>.<type>`. + +Example mappings: +``` +jack1.cv_in > jack1.midi_out.ch0.note3 +jack1.midi_in.ch0.pitch > jack1.cv_out +``` + +The MIDI subchannel syntax is intentionally kept compatible to the different MIDI backends also supported +by the MIDIMonster + +#### Known bugs / problems + +While JACK has rudimentary capabilities for transporting OSC messages, configuring and parsing such channels +with this backend would take a great amount of dedicated syntax & code. CV ports can provide fine-grained single +control channels as an alternative to MIDI. This feature may be implemented at some point in the future. |