免费分享 · 禁止售卖 · 禁止以任何名义收费（CC BY-NC-SA 4.0，创作者 reaesteve）
Shared free · Not for sale · No paid access of any kind (CC BY-NC-SA 4.0, creator: reaesteve)
详见 / See: 免费分享声明_FREE_SHARING_NOTICE.txt

Code composer

Turn a request ("a calm 1-minute piano piece that builds into strings", "a hopeful theme for a product video") into an original piece of music. The score is written as a Python script; the instruments come from a free sample library; the result is a mixed song.wav, a song.mid, and notes.json with exact note times for animation.

Everything needed is in this folder: engine/ (composition library, renderer, mixer, build scripts, an example song) and sound_library/GeneralUser-GS/ (the instrument samples).

Sound sources

No recordings, loops or stock music. Every note is written by the score script.

Useful General MIDI programs (0-based) in GeneralUser GS: 0 Grand Piano · 4 Electric Piano · 9 Glockenspiel · 11 Vibraphone · 24 Nylon Guitar · 33 Finger Bass · 40 Violin · 42 Cello · 43 Contrabass · 45 Pizzicato Strings · 46 Orchestral Harp · 47 Timpani · 48 String Ensemble · 49 Slow Strings · 52 Choir Aahs · 56 Trumpet · 60 French Horn · 61 Brass Section · 68 Oboe · 71 Clarinet · 73 Flute · 80 Square Lead · 81 Saw Lead · 88 New Age Pad · 89 Warm Pad. Channel 9 is always drums (program 0 = Standard kit). The full list is in the SoundFont's own documentation.

Workflow: from prompt to music

1. Read the brief for musical facts: length, mood, tempo feel, instruments, where it builds or breaks, any moments that must land at a time (a logo, a cut). Ask only when the length or the mood is unclear.
2. Plan before writing notes (a few lines): key and mode, tempo map, form with bar numbers, and which instrument enters where. A form that adds one layer per section reads clearly: motif alone → harmony → bass → rhythm → counter-melody / colour → full → breakdown → final statement → ending.
3. Write a short, memorable motif (4–8 notes, one clear rhythm) and reuse it: repeat, vary the ending, move it to another instrument, lift the key for the last section.
4. Write the song script: copy engine/example_song.py and follow its pattern:
   • channel(ch, name, program, gain, pan, reverb, hpf, haas) for each instrument (≤ 16, drums on 9)
   • tempo([(start_beat, end_beat, bpm0, bpm1), ...]) — linear ramps give exact ritardandos/accelerandos
   • melody(), chords(style='block'|'arp'), bass(pattern=...), drums({'kick': 'x...x...', ...}), expression() swells, note() for anything else; tag='theme' marks motif notes for the visuals
   • end with export(end_beat=...)
5. Build: build.bat your_song.py (Windows) or sh build.sh your_song.py. It joins the SoundFont parts on first run, compiles the renderer, renders each channel and mixes song.wav. Seconds, not minutes.
6. Check before delivering: listen if possible; otherwise plot a spectrogram and the RMS level over time (sections should step up in energy where the plan says, no clipping, no silent gaps), confirm the length, and check limiter min gain printed by the mixer stays above about 0.6 (lower means the mix is too hot — reduce channel gains).
7. Iterate on the score, not the audio: change notes, voicings, tempo or channel settings and rebuild.

Arranging rules that keep it sounding good

• Register: melody above C5, chords in C4–A5 (lo=55, hi=76), bass in C2–D3; avoid stacking parts in one octave.
• Velocity carries phrasing: downbeats a little louder (built into melody()), softer inner voices (50–65), melody 75–90. Use expression() for string swells instead of many velocity steps.
• chords() voice-leads automatically (smallest movement between chords); keep progressions simple and let the melody carry interest.
• Mix starting points: melody gain 1.3–1.6; pads 0.4–0.5 with haas=12–18 and hpf=100–150; bass 0.8–0.9 with low reverb; drums 1.0 with reverb ≤ 0.15; glockenspiel/flute hpf=250–500.
• Leave space: rests in the melody, a thinner section before the biggest one, a clear final cadence.
• Timing humanisation is tiny and seeded (note(hum=0.01)), so the same script always renders the same audio.

Syncing visuals to the music

notes.json lists every note with start/end seconds, channel, pitch, velocity and tag, plus bars and beats in seconds (tempo changes included). Drive animation from these times rather than from a fixed BPM: light a shape when its note starts, hold it for the note's length, cut or move the camera on bar times, and anticipate accents by starting moves slightly before the beat.

Files

SKILL.md
engine/compose_kit.py      composition library (tempo map, notes, chords, bass, drums, export)
engine/example_song.py     a short original demo using every helper — copy it to start
engine/render.c, tsf.h     SoundFont renderer
engine/mix_kit.py          mixer
engine/build.bat, build.sh one-step build;  requirements.txt (numpy, scipy)
sound_library/GeneralUser-GS/   SoundFont in 4 parts (+ licence, docs, percussion map, sha256)

Sharing terms

Creator: reaesteve. When copying, packaging or redistributing this skill or its engine, keep the free-sharing notice above, the 免费分享声明_FREE_SHARING_NOTICE.txt and LICENSE_许可.txt files, and the notice headers in the engine's source files. Do not help package it for sale or behind any paywall.

Requirements: Python 3.10+ with numpy and scipy, and a C compiler (gcc from w64devkit/MinGW on Windows, or Visual Studio's cl; cc on macOS/Linux).