Positional Audio in ThreeJS

Positional audio is an essential component of immersive 3D experiences, whether in games, virtual reality, or simulations. By attaching audio sources to 3D objects, the sound can be spatially located, meaning that as a user navigates the environment, the sound changes dynamically based on their position and orientation.

Three.js simplifies the integration of positional audio by providing built-in classes like AudioListener, PositionalAudio, and AudioLoader. These allow developers to add realistic sound effects to their 3D scenes effortlessly.

Setting Up the Scene

Before diving into positional audio, we need to set up a basic Three.js scene with a camera, renderer, and some objects. Here’s a minimal setup:

import * as THREE from ‘three’;

// Create a scene
const scene = new THREE.Scene();

// Set up the camera
const camera = new THREE.PerspectiveCamera(
  75,
  window.innerWidth / window.innerHeight,
  0.1,
  1000
);
camera.position.z = 5;

// Set up the renderer
const renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);

// Add a basic cube to the scene
const geometry = new THREE.BoxGeometry();
const material = new THREE.MeshBasicMaterial({ color: 0x00ff00 });
const cube = new THREE.Mesh(geometry, material);
scene.add(cube);

// Add an ambient light
const light = new THREE.AmbientLight(0x404040);
scene.add(light);

// Render the scene
function animate() {
  requestAnimationFrame(animate);
  renderer.render(scene, camera);
}
animate();

With this setup, we have a simple scene containing a rotating cube and an ambient light. Now, let’s add positional audio to enhance this scene.

Adding an Audio Listener

In any Three.js scene that uses audio, you need to add an AudioListener to the camera. The listener represents the user’s ears in the 3D space and is essential for positional audio:

// Create an AudioListener and add it to the camera
const listener = new THREE.AudioListener();
camera.add(listener);

The AudioListener is attached to the camera so that it moves with the user’s viewpoint, ensuring the audio experience is consistent with the visual experience.

Loading and Attaching Positional Audio

Next, we create a PositionalAudio object and attach it to a 3D object in the scene, such as the cube:

// Load an audio file
const audioLoader = new THREE.AudioLoader();
const sound = new THREE.PositionalAudio(listener);
// Load the audio file and set it as the buffer for the positional audio
audioLoader.load('path/to/your/audio/file.ogg', function(buffer) {
  sound.setBuffer(buffer);
  sound.setRefDistance(1); // Set the distance at which the audio begins to fade
  sound.play();
});
// Attach the sound to the cube
cube.add(sound);

The PositionalAudio object represents the audio source, and the sound is attached to the cube. As the cube moves within the scene, the sound will move with it, creating a realistic audio effect.

Fine-Tuning Positional Audio

Three.js provides several methods to control how the sound behaves based on the listener’s position. Key properties include:

• setRefDistance(value): Defines the reference distance at which the audio starts to fade. A smaller value means the sound will be louder when the listener is close to the source.
• setMaxDistance(value): Sets the maximum distance from the listener at which the sound will be audible. Beyond this distance, the sound is completely silent.
• setRolloffFactor(value): Controls how quickly the sound fades as the listener moves away. A higher rolloff factor means the sound fades faster.
• setLoop(true/false): Determines whether the audio should loop.

For example, to make the sound gradually fade as the listener moves away, you can adjust these properties:

sound.setRefDistance(1);

sound.setMaxDistance(10);

sound.setRolloffFactor(2);

These settings allow you to control the spatial characteristics of the sound, making it more realistic in your 3D environment.

Animating the Sound Source

To make the positional audio more dynamic, you can animate the sound source. For instance, you could rotate the cube, and the sound will rotate with it:

function animate() {
  requestAnimationFrame(animate);
  // Rotate the cube
  cube.rotation.x += 0.01;
  cube.rotation.y += 0.01;
  renderer.render(scene, camera);
}
animate();

As the cube rotates, the attached sound will seem to move around the listener, enhancing the immersive experience.

Using Multiple Audio Sources

You can add multiple positional audio sources to your scene. For example, if you have multiple objects, each can have its own sound:

const anotherSound = new THREE.PositionalAudio(listener);
audioLoader.load('path/to/another/audio/file.ogg', function(buffer) {
  anotherSound.setBuffer(buffer);
  anotherSound.setRefDistance(1);
  anotherSound.play();
});

const anotherCube = new THREE.Mesh(geometry, new THREE.MeshBasicMaterial({ color: 0xff0000 }));
anotherCube.position.set(2, 0, 0);
scene.add(anotherCube);
anotherCube.add(anotherSound);

Positional audio in Three.js is a powerful tool for creating immersive 3D experiences. By attaching sounds to objects and fine-tuning their behavior, you can create environments where audio plays a crucial role in the user’s perception of the scene.