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Using MIDI Input

Intermediate Composer

Connect a MIDI controller or keyboard to drive a synthesizer via MidiInput and FmSynth.

What you'll build

A polyphonic synthesizer playable from a MIDI keyboard or controller — MidiInput translating hardware note data into Vivid's internal note stream, driving FmSynth.

Operators used

Operator Domain Role
MidiInput Control Translates hardware MIDI into a notes_out lane stream
FmSynth Audio Two-operator FM synthesis with per-voice ADSR
Gain Audio Master volume
audio_out — Audio output

Step 1: Connect your MIDI device

Make sure your MIDI device is connected and recognized by macOS before adding MidiInput.

Add MidiInput. In the inspector: - channel — set to 0 for omni (receive all channels), or a specific channel (1–16) - mode — poly for polyphonic play (multiple simultaneous notes)

MidiInput does not produce audio — it produces a notes_out lane stream, which is Vivid's internal note format used by all synthesizers.

Step 2: Add FmSynth

Add FmSynth. Connect midi1/notes_out → fm1/notes_in.

Connect fm1/output → audio_out/input.

Play a note on your keyboard. You should hear the FM synth respond.

Step 3: Add Gain for volume control

Add Gain between FmSynth and the output. Connect fm1/output → gain1/input, gain1/output → audio_out/input. Set gain to 0.7.

Step 4: Tune the FM synthesis

FmSynth uses classic two-operator FM: a carrier oscillator modulated by a modulator oscillator.

Core params: - mod_ratio — frequency ratio of modulator to carrier. Integer ratios (1, 2, 3) produce harmonic timbres; non-integer ratios produce inharmonic, bell-like tones - mod_index — depth of frequency modulation. Low values (0–1) = subtle FM coloring; high values (5–20) = bright, complex harmonics - carrier_freq — base carrier frequency (overridden by MIDI note pitch)

ADSR envelope: - attack — time to reach full amplitude after note-on - decay — time to fall from peak to sustain level - sustain — amplitude while note is held - release — time to fade after note-off

Step 5: Add reverb

Insert Reverb between Gain and the output for a natural space. Set mix to 0.25 for subtle room ambience.

What's happening

MIDI device → MidiInput → notes_out (lane stream)
                                   ↓
                              FmSynth/notes_in
                                   ↓
                           voices_out (polyphonic audio)
                                   ↓
                               Gain → audio_out

notes_out is a lane-bearing stream: each active note is a lane, carrying pitch, velocity, gate, and pressure data. FmSynth spawns a voice per lane, mixing them down into a single stereo audio buffer via voices_out.

The polyphony limit is set by FmSynth's voice count. Voices are allocated on note-on and released on note-off after the release envelope completes.

Tip: Use MidiInput outputs for modulation

MidiInput also exposes individual scalar outputs: velocity, gate, mod_wheel, pitch_bend, cc_value. These are Control-domain values and can wire to any parameter.

For example: midi1/mod_wheel → fm1/mod_index_cv maps the modwheel to FM depth in real time.

Next steps