MIDI Event Generation

Overview

Beyond receiving MIDI events through callbacks like onNote and onController, uvi-script can also generate outgoing MIDI events. This is useful for building arpeggiators, chord generators, MIDI processors, and automation scripts.

There are two approaches:

• Helper functions — concise, dedicated functions for each event type
• postEvent() — low-level, allows full control over all event fields

Helper Functions

These convenience functions wrap postEvent with the correct event type. All accept optional channel and input parameters for routing to specific Parts.

Control Change

Send a MIDI CC message:

function onNote(e)
    postEvent(e)
    -- send mod wheel (CC1) value 100 on the same channel
    controlChange(1, 100, e.channel)
end
 
-- reset all controllers on note release
function onRelease(e)
    for cc = 1, 127 do
        controlChange(cc, 0)
    end
end

See also

controlChange, onController

Pitch Bend

Send a pitch bend message. The value is normalized to [-1.0; 1.0]:

-- pitch bend ramp on each note
function onNote(e)
    postEvent(e)
    spawn(function()
        for i = 0, 100 do
            pitchBend(i / 100)  -- ramp from 0 to +1
            wait(10)
        end
        pitchBend(0)  -- reset
    end)
end

See also

pitchBend, onPitchBend

Program Change

Send a program change message:

-- switch program based on velocity range
function onNote(e)
    if e.velocity > 100 then
        programChange(1)  -- high velocity: program 1
    else
        programChange(0)  -- low velocity: program 0
    end
    postEvent(e)
end

See also

programChange, onProgramChange

Aftertouch

Send channel aftertouch or polyphonic aftertouch:

-- convert velocity to channel aftertouch
function onNote(e)
    postEvent(e)
    afterTouch(e.velocity)
end
 
-- per-note pressure from velocity
function onNote(e)
    postEvent(e)
    polyAfterTouch(e.velocity, e.note)
end

See also

afterTouch, polyAfterTouch, onAfterTouch, onPolyAfterTouch

Modifying Incoming Events

Instead of generating new events, you can modify incoming events before forwarding them with postEvent. This is the most efficient way to transform MIDI data:

-- Remap CC1 (mod wheel) to CC11 (expression)
function onController(e)
    if e.controller == 1 then
        e.controller = 11
    end
    postEvent(e)
end

You can modify any field of the event table before posting it:

-- Transpose all notes up one octave
function onNote(e)
    e.note = e.note + 12
    postEvent(e)
end
 
function onRelease(e)
    e.note = e.note + 12
    postEvent(e)
end

Note

When modifying onNote events, remember to apply the same transformation in onRelease so the engine can match the note-off to the correct voice.

Using postEvent Directly

The helper functions are shortcuts for postEvent. You can achieve the same result (and more) by constructing event tables directly:

-- these two are equivalent:
controlChange(1, 64)
 
postEvent({type = Event.ControlChange, controller = 1, value = 64})

Using postEvent directly gives access to additional fields like layer and delta (timing offset in ms):

-- send CC to a specific layer with a 10ms delay
postEvent({
    type = Event.ControlChange,
    controller = 1,
    value = 100,
    layer = 2
}, 10)

Raw MIDI with postMidiEvent

For playback of MIDI files or raw MIDI data, use postMidiEvent with MidiEvent objects:

local event = MidiEvent(0, Event.NoteOn, 0, 60, 100)
postMidiEvent(event)

Note

Events posted via postMidiEvent don't have voice IDs. For advanced voice tracking, use playNote and releaseVoice instead.

See also

MIDI, Events, Event Callbacks, Asynchronous Operations