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8BEETY

Turn any MIDI file into music that sounds like it came out of an NES, a Game Boy, a Super Nintendo, or a Sega Genesis — in your browser, in seconds, with no login and no server.

Drop in a .mid, and the auto-arranger assigns your tracks to real chip channels: melodies to the pulse channels, bass to the triangle (or the Game Boy's wavetable), drums to the noise LFSR. Chords become fast arpeggios — the way NES composers actually did it — and everything is compiled to a frame-by-frame register script played by an authentic sound model in an AudioWorklet.

Try it: https://www.8beety.com

Features

• Four chips, switchable mid-playback from one dropdown:
  • NES 2A03 — nonlinear mixer, console output filter, authentic timer-quantized detune
  • Game Boy DMG — four wavetable presets, 64 Hz envelope quantization, true stereo with per-channel hard pan
  • SNES SPC700 style — eight sample voices from a procedurally generated bank (strings, e.piano, brass, choir…) with BRR-flavored grit and the console's signature stereo echo
  • Sega Genesis YM2612 style — five lanes of genuine 4-operator FM synthesis (the chip's eight algorithms, real fnum/block pitch quantization) plus 8-bit DAC drums
• Polyphony done the 8-bit way: top/bottom note extraction, compiler-generated arpeggios with chord-tone reduction, split-across-channels mode, and pulse-layer modes (double, detune, echo, octave).
• A real GM drum map: kick, snare, three tom tiers, hats, crash, ride, metal hit — priority-resolved onto the noise channel, or onto sampled kits on the 16-bit chips.
• FamiTracker-style instruments: per-frame volume/duty/pitch/arpeggio macros, plus quick tweaks (duty, attack/decay, vibrato) without a macro editor. FM patches and sampled instruments on the 16-bit chips.
• Regions: split a track at any bar and give bars 17–32 a different instrument, channel, or poly mode.
• Chord Assist: detects your key and chords, enriches triads with diatonic 7ths/9ths/sus, and offers substitute progressions from the free-midi-chords corpus, voiced for the chip.
• Video export: a 9:16 MP4 ready for TikTok/Shorts — your song scrolling DAW-style across the screen of a drawn Game Boy (NES/GB), or above an SNES- or Genesis-style console with the song title on the cartridge label (16-bit chips). Survives background tabs, stays QuickTime-safe.
• Export & share: 16-bit WAV (44.1/48 kHz, optional loop 2× + fade, sample-identical to playback; stereo on stereo chips), self-contained project JSON, arranged MIDI (arps written out as fast notes), and share links that pack the whole project into the URL.

Development

npm install
npm run dev        # local dev server
npm test           # vitest (engine, compiler, DSP, theory — ~300 tests)
npm run build      # production build (dist/)
npm run lint

Developer-only scripts:

node scripts/make-demo-midis.mjs                          # regenerate the demo songs
python3 scripts/build_chord_library.py path/to/free-midi-chords   # rebuild the chord library

The spec (SPEC.md) is the source of truth for the architecture; CLAUDE.md holds the working conventions; the design docs and implementation plans the app was built from are preserved under docs/superpowers/. The audio engine lives in src/audio/apu-worklet.ts (shared by realtime playback, offline WAV rendering, and the Node test suite), the pure compiler in src/engine/compile.ts.

To enable the "Buy me a coffee" link, set COFFEE_URL in src/config.ts.

Learn how this was built

This entire application was built by one person directing an AI coding assistant, spec-first and milestone by milestone. The internet-menace-template/ folder packages the project as a beginner-friendly prompt-engineering guide — the design spec, how it works, how to host it, and the seven lessons behind the method. The guide is also available at internetmenace.com.

Credits

• Chord progressions derived from ldrolez/free-midi-chords (MIT)
• NES APU documentation: NESdev wiki
• Game Boy audio documentation: Pan Docs
• SNES and Genesis audio background: SFC Development Wiki and Sega Retro

Not affiliated with Nintendo or Sega. No Nintendo or Sega assets are used or imitated.

License

MIT © 2026 Shane Morris