MIDI Engine¶

How it works¶

The MIDI engine uses pyFluidSynth to render audio directly to your speakers. No DAW, no external synth, no virtual MIDI routing. One process, one SoundFont file, sound comes out.

Classifier output ──► MidiController ──► FluidSynth ──► Speakers
                      (thread-safe)     (multiple drivers)

The engine is highly portable on Windows, automatically attempting to initialize using WASAPI (preferred for low latency), DirectSound, or WaveOut.

Quick start¶

from midi_engine import MidiController

controller = MidiController()
controller.start()

# From the classifier loop:
controller.on_classification(
    right_hand="palm_up_out",   # chord
    left_hand="fist_down_out",  # instrument
    amplitude=0.73              # EMG amplitude -> volume
)

controller.stop()

Chords¶

All 7 chords use full guitar-style voicings (not just triads):

Chord	MIDI Notes	Pitches
C	48, 52, 55, 60, 64, 67	C3 E3 G3 C4 E4 G4
Am	45, 52, 57, 60, 64	A2 E3 A3 C4 E4
Em	40, 47, 52, 55, 59, 64	E2 B2 E3 G3 B3 E4
G	43, 47, 50, 55, 59, 67	G2 B2 D3 G3 B3 G4
Dm	38, 50, 53, 57, 62	D2 D3 F3 A3 D4
F	41, 48, 53, 57, 60, 65	F2 C3 F3 A3 C4 F4
D	38, 45, 50, 54, 57, 62	D2 A2 D3 F#3 A3 D4

Instruments¶

Name	GM Program	Gesture
Piano	0	`fist_down_out`
Nylon Guitar	24	`palm_up_out`
Steel Guitar	25	`palm_down_out`
Electric Guitar	27	`palm_down_up`
Strings	48	`fist_down_up`
Pad (Warm)	88	`peace_out`

Chord progression mode¶

Lock to a song so gestures advance through the chord sequence:

controller.set_progression("save_your_tears")              # full song
controller.set_progression("careless_whisper", section="verse")  # just verse
controller.clear_progression()                               # free-play

See the Playlist page for all available songs.

Tuning parameters¶

Parameter	Default	Effect
`strum_delay_ms`	15	Delay between notes in a chord (guitar strum effect). Set to 0 for block chords.
`debounce_frames`	3	Consecutive same-gesture frames required before triggering. Increase if classifier is noisy.
`gain`	0.8	Master volume (0.0 to 1.0+).

Velocity Mapping

EMG amplitude (0.0 to 1.0) is linearly mapped to MIDI velocity values between 40 and 127. This ensures even soft gestures produce audible sound while allowing for dynamic expression.

Velocity updates dynamically during sustain — if you squeeze harder while holding a chord, the notes are re-voiced at the new velocity in real time.

controller = MidiController(strum_delay_ms=25, debounce_frames=5, gain=1.0)

Other useful methods¶

Method	Description
`set_instrument("piano")`	Switch instrument directly
`play_chord("Am", velocity=90, duration=1.0)`	Play a chord (blocks the calling thread)
`play_chord("Am", blocking=False)`	Play a chord without blocking (notes auto-stop after duration)
`play_note(60, velocity=100, duration=0.5)`	Play a single MIDI note
`play_note(60, blocking=False)`	Play a note without blocking
`panic()`	All notes off (emergency stop)
`get_state()`	Returns dict with current chord, instrument, progression position