AudioContext.createBuffer()

Syntax

var audioCtx = new AudioContext();
var buffer = audioCtx.createBuffer(2, 22050, 44100);

Parameters

numOfChannels

An integer representing the number of channels this buffer should have. Implementations must support a minimum 32 channels.

length

An integer representing the size of the buffer in sample-frames.

sampleRate

The sample-rate of the linear audio data in sample-frames per second. An implementation must support sample-rates in at least the range 22050 to 96000.

Returns

An AudioBuffer.

Examples

First, a couple of simple trivial examples, to help explain how the parameters are used:

var audioCtx = new AudioContext();
var buffer = audioCtx.createBuffer(2, 22050, 44100);

If you use this call, you will get a stereo buffer (two channels), that, when played back on an AudioContext running at 44100Hz (very common, most normal sound cards run at this rate), will last for 0.5 seconds: 22050 frames / 44100Hz = 0.5 seconds.

var audioCtx = new AudioContext();
var buffer = audioCtx.createBuffer(1, 22050, 22050);

If you use this call, you will get a mono buffer (one channel), that, when played back on an AudioContext running at 44100Hz, will be automatically *resampled* to 44100Hz (and therefore yield 44100 frames), and last for 1.0 second: 44100 frames / 44100Hz = 1 second.

Now let's look at a more complex createBuffer() example, in which we create a two second buffer, fill it with white noise, and then play it via an AudioBufferSourceNode. The comment should clearly explain what is going on. You can also run the code live, or view the source.

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

pre.innerHTML = myScript.innerHTML;

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

var myAudioBuffer = audioCtx.createBuffer(channels, frameCount, audioCtx.sampleRate);

button.onclick = function() {
  // Fill the buffer with white noise;
  //just random values between -1.0 and 1.0
  for (var channel = 0; channel < channels; channel++) {
   // This gives us the actual ArrayBuffer that contains the data
   var nowBuffering = myAudioBuffer.getChannelData(channel);
   for (var 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
  var source = audioCtx.createBufferSource();
  // set the buffer in the AudioBufferSourceNode
  source.buffer = myAudioBuffer;
  // connect the AudioBufferSourceNode to the
  // destination so we can hear the sound
  source.connect(audioCtx.destination);
  // start the source playing
  source.start();
}

Specifications

Browser compatibility

See also

• Using the Web Audio API