midi-sketch-bach

Alpha — This project is under active development. Features and APIs may change. Pre-built binaries are coming soon.

🎹 Try it now: bach.midi-sketch.libraz.net — generate and play Bach-style pieces right in your browser (WebAssembly). Full documentation and a counterpoint course live on the same site.

A MIDI generator dedicated to the instrumental works of Johann Sebastian Bach.

Bach's instrumental music — organ fugues, solo string suites, chamber sonatas — is built on an extraordinary architecture of counterpoint, harmonic logic, and formal structure. This project focuses exclusively on these instrumental works, and attempts to reproduce their structural principles — strict voice-leading, the harmonic flow of the cello suites, the polyphonic texture of organ fugues — as playable MIDI, as closely as possible.

There are still many known issues across counterpoint rules, voice-leading, and musical structure. Contributions and feedback are welcome.

Built on the development insights from midi-sketch, a pop/contemporary music generator. Available as a CLI tool, JavaScript/WASM library, and interactive web demo.

What It Generates

Organ Works — counterpoint-driven, multi-voice:

Form	After the manner of	Voices
Prelude and Fugue	BWV 532, 548	3
Fugue	Strict 3-voice fugue	3
Trio Sonata	BWV 525-530	3
Chorale Prelude	BWV 599-650 (Orgelbüchlein)	3
Toccata and Fugue	BWV 565	3
Passacaglia	BWV 582	3
Fantasia and Fugue	BWV 537, 542	3

Solo String Works — harmony-driven, single line:

Form	After the manner of	Instrument
Cello Prelude	BWV 1007 (Suite No.1)	Cello
Chaconne	BWV 1004 (Partita No.2)	Violin

Keyboard Works — variation form:

Form	After the manner of	Voices
Goldberg Variations	BWV 988	3

Every fugue enforces proper exposition, real/tonal answer, countersubject, episodes, and stretto. Parallel fifths and octaves are forbidden. Voice crossing is resolved.

Quick Start

CLI

make build
./build/bin/bach_cli                                        # Prelude and Fugue in C major
./build/bin/bach_cli --form fugue --key g_minor --seed 42
./build/bin/bach_cli --form chaconne --scale full
./build/bin/bach_cli --form cello_prelude --bpm 120 -o prelude.mid

JavaScript / WASM

import { init, BachGenerator } from '@libraz/midi-sketch-bach';

await init();
const bach = new BachGenerator();
bach.generate({ form: 'fugue', key: 0, isMinor: true, seed: 42 });

const midi = bach.getMidi();     // Uint8Array
const events = bach.getEvents(); // parsed JSON with note data
bach.destroy();

Web Demo

Hosted: bach.midi-sketch.libraz.net — or run locally:

make demo   # http://localhost:8080/demo/

CLI Options

Option	Description	Default
--form FORM	Composition form	prelude_and_fugue
--key KEY	Key (e.g. g_minor, D_major)	C_major
--character CH	severe, playful, noble, restless	auto
--instrument INST	organ, harpsichord, piano, violin, cello, guitar	auto
--scale SCALE	short, medium, long, full	short (medium for fugue)
--bars N	Target bar count (overrides --scale)	-
--bpm N	Tempo (40-200)	72
--seed N	Random seed (0 = random)	0
--json	Output JSON event data	-
--generated-json	Output generated.v1 + provenance.v1 JSON	-
--free-counterpoint	Experimental: generate the inner voice via scored search (off by default)	-
-o FILE	Output path	output.mid

Build

make build          # C++ CLI
make test           # Run C++ tests (980+ via ctest)
yarn test           # Run JS/WASM tests (210+ via vitest)
make quality-gate   # Format + build + test
make wasm           # WASM + JS bindings

Requires: C++17 compiler, CMake 3.15+. WASM build requires Emscripten.

License

AGPL-3.0 / Commercial dual license. Free to use, modify, and redistribute under AGPL-3.0; embedding in closed-source products or proprietary SaaS requires a commercial license. For commercial inquiries: libraz@libraz.net