Add Onset2Midi plugin: Onset detector to MIDI note trigger

[federico-de-lellis]

Summary

Adds Onset2Midi plugin that uses Essentia's OnsetDetection to convert audio onsets into MIDI note events in real time, that can be creatively used to drive a sampler on the next track from a live or recorded percussive signal.

The plugin is a CMake plugin and follows the same structure and visual style as the existing plugins in the repo.

What it does

• Detects percussive onsets per frame and emits a fixed MIDI note, with velocity derived from the hit strength.
• DSP chain (1024-sample frame, 512 hop): mono frame → Windowing (Hann) → FFT → CartesianToPolar → OnsetDetection → onset-detection function → adaptive peak-picking → MIDI.
• Produces MIDI output (NEEDS_MIDI_OUTPUT), so route it to an instrument/sampler track.
• A live activity LED in the UI flashes on every detected onset.

Controls

Detection

• Onset Method selectable Essentia onset-detection function: HFC / Complex / Flux / MelFlux / RMS / Complex Phase
• Sensitivity (0-1) adaptive peak-pick threshold
• Min Inter-Onset (5-500 ms) debounce window to avoid double-triggers

MIDI

• MIDI Note (0-127, default 60)
• MIDI Channel (1-16, default 10 GM drum channel)
• Velocity Sensitivity (0.1-4.0) scales hit strength to MIDI velocity
• Note Hold (5-1000 ms) gate length before the scheduled note-off

Tested on

• macOS (VST3)
• Essentia built from source (build_external/)
• Built via CMake

Demo

Link to the video demo running in Ableton Live

UI