W3cubDocs

/Web APIs

AudioBuffer: getChannelData() method

The getChannelData() method of the AudioBuffer Interface returns a Float32Array containing the PCM data associated with the channel, defined by the channel parameter (with 0 representing the first channel).

Syntax

getChannelData(channel)

Parameters

channel: The channel property is an index representing the particular channel to get data for. An index value of 0 represents the first channel. If the channel index value is greater than of equal to AudioBuffer.numberOfChannels, an INDEX_SIZE_ERR exception will be thrown.

Return value

A Float32Array.

Examples

In the following example we create a two second buffer, fill it with white noise, and then play it via an AudioBufferSourceNode. The comments should clearly explain what is going on. You can also run the code live, or view the source.

const audioCtx = new (window.AudioContext || window.webkitAudioContext)();
const button = document.querySelector("button");
const pre = document.querySelector("pre");
const myScript = document.querySelector("script");

pre.innerHTML = myScript.innerHTML;

// Stereo
const channels = 2;
// Create an empty two second stereo buffer at the
// sample rate of the AudioContext
const frameCount = audioCtx.sampleRate * 2.0;

const myArrayBuffer = audioCtx.createBuffer(2, frameCount, audioCtx.sampleRate);

button.onclick = () => {
  // Fill the buffer with white noise;
  //just random values between -1.0 and 1.0
  for (let channel = 0; channel < channels; channel++) {
    // This gives us the actual ArrayBuffer that contains the data
    const nowBuffering = myArrayBuffer.getChannelData(channel);
    for (let i = 0; i < frameCount; i++) {
      // Math.random() is in [0; 1.0]
      // audio needs to be in [-1.0; 1.0]
      nowBuffering[i] = Math.random() * 2 - 1;
    }
  }

  // Get an AudioBufferSourceNode.
  // This is the AudioNode to use when we want to play an AudioBuffer
  const source = audioCtx.createBufferSource();
  // set the buffer in the AudioBufferSourceNode
  source.buffer = myArrayBuffer;
  // connect the AudioBufferSourceNode to the
  // destination so we can hear the sound
  source.connect(audioCtx.destination);
  // start the source playing
  source.start();
};

Specifications

Specification
Web Audio API # dom-audiobuffer-getchanneldata

Browser compatibility