Audio Composer — SFX + Music

Two-tier audio system: real AI-generated MP3s when ELEVENLABS_API_KEY is available, deterministic chiptune oscillator synthesis as a zero-cost fallback. The same AudioManager.js handles both transparently — no code change needed in Game.js.

When to use

Run in parallel with the art generation stages (sprite-artist, tile-artist, bg-artist), after GDD is finalized. Also run on an existing game when the user says "add sound", "add music", or "upgrade to ElevenLabs audio."

Two modes

Mode A — ElevenLabs (when ELEVENLABS_API_KEY is set)

Calls POST https://api.elevenlabs.io/v1/sound-generation for each SFX action. Uses the eleven_text_to_sound_v2 model with a genre-flavoured text prompt (e.g. "2D action platformer game, retro 8-bit jump sound, quick upward pitch sweep"). Saves MP3s to public/assets/sfx/<name>.mp3. Adds mp3Path to each entry in sfx.json. AudioManager.js preloads all MP3s as AudioBuffers via decodeAudioData and plays them on demand.

Rate limit: requests are made sequentially with automatic retry on HTTP 429.

Mode B — Web Audio oscillator (no API key, or --no-elevenlabs)

Writes oscillator parameters (freq, dur, type, vol) to sfx.json. AudioManager.js generates sound at runtime using OscillatorNode — no audio files, no network calls, works offline.

Output contract

public/assets/sfx.json         — SFX descriptors (always written)
public/assets/music.json       — music loop: BPM + pentatonic note sequence
public/assets/sfx/<name>.mp3   — real audio files (Mode A only)
src/audio/AudioManager.js      — fixed runtime template (never regenerated)

game-state.json gains state.audio:

{
  "audio": {
    "sfxPath": "assets/sfx.json",
    "musicPath": "assets/music.json",
    "managerPath": "src/audio/AudioManager.js",
    "elevenlabs": true,       // true when Mode A ran
    "mp3Count": 6             // number of MP3s successfully generated
  }
}

sfx.json shape

Mode A (with MP3):

{
  "jump": { "freq": 380, "dur": 0.14, "type": "square", "vol": 0.22, "mp3Path": "assets/sfx/jump.mp3" }
}

Mode B (oscillator only):

{
  "jump": { "freq": 380, "dur": 0.14, "type": "square", "vol": 0.22 }
}

AudioManager.play('jump') checks for mp3Path first; if missing or load fails, falls back to the oscillator params. Per-sound graceful degradation — a failed ElevenLabs response for one SFX doesn't break the rest.

Genre presets

AudioManager usage (codesmith adds these)

import AudioManager from '../audio/AudioManager.js';

// In create():
AudioManager.init(this);        // registers Safari AudioContext unlock

// In event handlers / overlaps:
AudioManager.play('jump');      // plays MP3 if available, oscillator if not
AudioManager.play('pickup');
AudioManager.play('hit');
AudioManager.play('death');
AudioManager.play('win');
AudioManager.stopMusic();       // call on game-over

// Optional:
AudioManager.mute();
AudioManager.unmute();

Safari iOS compatibility

AudioManager.init(scene) registers one-shot pointerdown and keydown listeners that create and unlock the AudioContext on first interaction. MP3 buffers are decoded at that point. This satisfies Safari iOS's user-gesture requirement without any extra plumbing in Game.js.

Process

1. Read game-state.json → gdd.genre.
2. Run scripts/compose_audio.mjs <project-dir>.
   • If ELEVENLABS_API_KEY is set: generate MP3s, fallback per-sound on error.
   • Otherwise: oscillator-only mode.
3. Patch game-state.json with state.audio.
4. Codesmith reads state.audio and adds import AudioManager + AudioManager.init(this) to Game.js.

Scripts

• scripts/compose_audio.mjs <project-dir> [--bpm N] [--no-elevenlabs]
  • --no-elevenlabs — force oscillator mode even if the key is set
  • --bpm N — override music tempo