producer-control-bus.md

Producer Control Bus v1

The Producer Control Bus is a loose MIDI CC contract. Senders and receivers do not link against each other, share project state, or require a particular host. Every receiver remains usable through its panel and ordinary host automation.

Default addresses

CC	Meaning	Receiver
19	Acquire at 127; release at 0	All bus receivers
20–27	Normalized channel gain overlays	T-Mix channels 1–8
30	Delay time or synchronized-length selection	Loopdelay
31	Delay feedback	Loopdelay
32	Reverb wet mix	Lightverb
33	Reverb space	Lightverb
34	Duck depth overlay	Bassops (MIDI input not yet enabled)
35	Wet/dry blend	Bassops (MIDI input not yet enabled)

Payload values are absolute 0–127 values. Receivers own smoothing, range mapping, and safety limits. Producer values are transient overlays and never replace the receiver's saved manual setting.

Ownership and compatibility

Mixgen sends CC 19 value 127 before its first payload. Stopping or disabling the producer sends CC 19 value 0 and unity values for T-Mix CC 20–27. Changing the output channel releases the old channel before acquiring the new one.

Each receiver has a Control channel setting: 0 is Omni and 1–16 selects one MIDI channel. Require CC 19 gate rejects payload until ownership has been acquired. It defaults off, preserving direct control from older projects and ordinary hardware. The receiver's Release action always returns to saved manual values.

T-Mix, Loopdelay, and Lightverb expose MIDI output and forward incoming events unchanged. This permits one stream to travel through a serial effect chain in hosts that model MIDI as a plugin-to-plugin pipeline.

Mixgen routing

Mixgen provides T-Mix, FX-only, and Full-bus profiles. Its four effect macros default to CC 30–33. Each macro chooses one of the eight musical pattern lanes, a destination CC, minimum and maximum normalized values, and optional inversion. These are data-driven mappings: changing a destination allows the same producer to control a third-party effect without changing its engine.

The default profile remains T-Mix-only for existing projects. Choose Full bus to emit CC 20–33 together. Inverted default FX lanes make delay and reverb rise when their source mix lane recedes.

Audio-sidechain receivers

Not all bus-adjacent plugins use MIDI CC as their primary control input. Bassops accepts a dedicated audio sidechain on inputs 3–4 (typically a dry kick-drum send): an internal envelope follower drives a VCA over the main signal on inputs 1–2. Its core ducking behaviour therefore works without any bus connection.

However, Bassops parameters can be overlaid by the bus once MIDI input is enabled (requires DISTRHO_PLUGIN_WANT_MIDI_INPUT 1 in the build):

CC	Parameter	Effect
34	Duck Depth	Deepen or soften the sidechain duck in real time
35	Wet	Blend the processed signal in or out

Adding Bassops after a T-Mix or Loopdelay in the signal chain keeps the CC 19 gate and audio MIDI-through working as usual.

Vocabulary

Profile files (.ttl) use the trn: prefix to describe bus participation. The following terms are in use across plugin profiles:

Term	Kind	Meaning
trn:ControlMidi	Port type	MIDI input/output carrying CC bus messages
trn:AudioSidechain	Port type	Audio input used as an amplitude control source via an envelope follower, not audio-to-process
trn:BusProducer	trn:busRole value	Plugin emits CC on the bus (e.g. Mixgen)
trn:BusReceiver	trn:busRole value	Plugin accepts CC parameter overlays from a bus producer
trn:ccMapping	Property	Declares a CC slot produced or consumed by the plugin
trn:ccGate	Boolean flag on trn:ccMapping	Marks the ownership-gate CC (19) as distinct from parameter-overlay CCs
trn:feedsControls	Property	Producer side: names specific downstream receiver plugins

trn:AudioSidechain and trn:BusProducer/trn:BusReceiver are extensions introduced to distinguish audio-envelope control from CC control, and to make bus membership machine-readable rather than inferred from ccMapping entries alone.