threejs-impl-audio

threejs-impl-audio

Quick Reference

Class Hierarchy

EventDispatcher
  └── Object3D
        ├── AudioListener    (receiver — attach to camera)
        ├── Audio            (non-positional — background music, UI sounds)
        └── PositionalAudio  (3D spatial — attached to scene objects)

Supporting classes:

• AudioLoader — loads audio files into AudioBuffer
• AudioAnalyser — real-time frequency analysis for visualization

Architecture Overview

Component	Role	Attach To
AudioListener	Virtual ear (Web Audio API destination)	Camera (ALWAYS)
Audio	Non-positional sound (same volume everywhere)	Any Object3D or scene
PositionalAudio	3D spatial sound (volume depends on distance)	Mesh or Object3D in scene
AudioLoader	Async audio file loader	N/A (utility)
AudioAnalyser	FFT frequency data extractor	Wraps an Audio instance

Critical Warnings

NEVER call sound.play() without first ensuring the AudioContext is resumed after user interaction. Modern browsers ALWAYS suspend the AudioContext until a user gesture (click, tap, keypress) occurs.

NEVER create more than one AudioListener per scene. Multiple listeners produce undefined spatialization behavior.

NEVER set autoplay = true and expect playback without user interaction. The browser WILL block it silently.

ALWAYS attach the AudioListener to the camera. If attached to another object, spatial audio calculations use the wrong reference position.

ALWAYS call listener.context.resume() inside a user interaction handler before playing any audio.

NEVER forget to handle the onError callback in AudioLoader.load(). Missing audio files fail silently without error handling.

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AudioListener Setup

The AudioListener is the scene's virtual microphone. It wraps the Web Audio API's AudioContext and AudioDestinationNode.

import * as THREE from 'three';

const listener = new THREE.AudioListener();
camera.add( listener ); // ALWAYS add to camera

Master Volume Control

listener.setMasterVolume( 0.8 ); // range [0, 1]
const vol = listener.getMasterVolume(); // returns 0.8

Global Audio Filter

const filter = listener.context.createBiquadFilter();
filter.type = 'lowpass';
filter.frequency.value = 1000;
listener.setFilter( filter );
// Later: listener.removeFilter();

---

Audio (Non-Positional)

Use Audio for background music, ambient soundscapes, and UI feedback sounds. Volume is identical regardless of listener position.

Loading and Playing

const sound = new THREE.Audio( listener );
const audioLoader = new THREE.AudioLoader();

audioLoader.load( 'music.mp3', ( buffer ) => {
    sound.setBuffer( buffer );
    sound.setLoop( true );
    sound.setVolume( 0.5 );
    // Do NOT call sound.play() here — wait for user interaction
});

Autoplay Policy Compliance (MANDATORY)

document.addEventListener( 'click', () => {
    if ( listener.context.state === 'suspended' ) {
        listener.context.resume();
    }
    if ( !sound.isPlaying ) {
        sound.play();
    }
}, { once: true } );

Playback Control

sound.play();                    // start playback
sound.pause();                   // pause (resume with play())
sound.stop();                    // stop and reset to beginning
sound.setPlaybackRate( 1.5 );   // 1.5x speed
sound.setDetune( -100 );        // pitch down 1 semitone (100 cents)

Alternative Sources

// HTML5 media element (for streaming large files)
const audioEl = new Audio( 'long-track.mp3' );
sound.setMediaElementSource( audioEl );

// Microphone input
navigator.mediaDevices.getUserMedia( { audio: true } ).then( ( stream ) => {
    sound.setMediaStreamSource( stream );
});

---

PositionalAudio (3D Spatial)

Use PositionalAudio for sounds that exist at a location in the scene. Volume and stereo panning change based on the listener's distance and orientation.

Basic Setup

const positionalSound = new THREE.PositionalAudio( listener );

audioLoader.load( 'engine.ogg', ( buffer ) => {
    positionalSound.setBuffer( buffer );
    positionalSound.setRefDistance( 20 );
    positionalSound.setRolloffFactor( 1 );
    positionalSound.setDistanceModel( 'inverse' );
    positionalSound.setLoop( true );
    positionalSound.setVolume( 0.5 );
});

mesh.add( positionalSound ); // sound position follows the mesh

Distance Model Decision Tree

Model	When to Use	Behavior
'inverse' (default)	Realistic environments	Gradual rolloff; NEVER reaches zero
'linear'	Controlled radius (e.g., room-based)	Volume drops to zero at maxDistance
'exponential'	Dramatic close/far contrast	Steep falloff curve

Choosing parameters:

• refDistance — Distance at which volume is 100%. Set to the "comfortable listening range" in scene units. Typical: 1 to 20.
• maxDistance — ONLY matters for 'linear' model. Ignored by 'inverse' and 'exponential'.
• rolloffFactor — Speed of volume decrease. For 'inverse': 1 = realistic. For 'linear': 1 = full range. Higher values = faster rolloff.

Directional Audio Cone

positionalSound.setDirectionalCone( 180, 360, 0.1 );
// coneInnerAngle: 180° — full volume zone
// coneOuterAngle: 360° — transition zone
// coneOuterGain: 0.1  — volume outside outer cone (10%)

---

AudioLoader

ALWAYS use AudioLoader to load audio files. It returns an AudioBuffer via callback.

const loader = new THREE.AudioLoader();

loader.load(
    'sound.ogg',
    ( buffer ) => { sound.setBuffer( buffer ); },   // onLoad
    ( xhr ) => { console.log( (xhr.loaded / xhr.total * 100) + '% loaded' ); }, // onProgress
    ( err ) => { console.error( 'Audio load failed:', err ); }  // onError — ALWAYS handle
);

Supported formats: MP3, OGG, WAV, AAC. OGG has the best compression-to-quality ratio but is NOT supported in Safari. ALWAYS provide MP3 as a fallback for cross-browser compatibility.

---

AudioAnalyser

Wraps the Web Audio API's AnalyserNode for real-time frequency visualization.

const analyser = new THREE.AudioAnalyser( sound, 256 );
// fftSize MUST be a power of 2: 32, 64, 128, 256, 512, 1024, 2048

function animate() {
    requestAnimationFrame( animate );

    const data = analyser.getFrequencyData();    // Uint8Array, length = fftSize / 2
    const avg = analyser.getAverageFrequency();  // number (0-255)

    // Drive visuals from audio data
    mesh.scale.y = 1 + avg / 128;
    renderer.render( scene, camera );
}

Frequency Data Details

• getFrequencyData() returns a Uint8Array with fftSize / 2 elements
• Each element ranges from 0 to 255 (decibel magnitude)
• Index 0 = lowest frequency, last index = highest frequency
• getAverageFrequency() returns the arithmetic mean of all bins

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Integration Checklist

1. Create ONE AudioListener and add it to the camera
2. Create Audio or PositionalAudio with the listener
3. Load audio with AudioLoader
4. Set buffer, volume, loop, and distance properties
5. Add user interaction handler to resume AudioContext
6. Call play() ONLY after user interaction
7. For spatial audio: add PositionalAudio as child of the target mesh

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Reference Links

• references/methods.md -- Complete API signatures for AudioListener, Audio, PositionalAudio, AudioLoader, AudioAnalyser
• references/examples.md -- Working code examples for common audio scenarios
• references/anti-patterns.md -- What NOT to do with Three.js audio

Official Sources

• https://threejs.org/docs/#api/en/audio/AudioListener
• https://threejs.org/docs/#api/en/audio/Audio
• https://threejs.org/docs/#api/en/audio/PositionalAudio
• https://threejs.org/docs/#api/en/audio/AudioAnalyser
• https://threejs.org/docs/#api/en/loaders/AudioLoader