The getByteFrequencyData() method of the AnalyserNode interface copies the current frequency data into a Uint8Array (unsigned byte array) passed into it.

If the array has fewer elements than the AnalyserNode.frequencyBinCount, excess elements are dropped. If it has more elements than needed, excess elements are ignored.


var audioCtx = new AudioContext();
var analyser = audioCtx.createAnalyser();
var dataArray = new Uint8Array(analyser.frequencyBinCount); // Uint8Array should be the same length as the frequencyBinCount 
analyser.getByteFrequencyData(dataArray); // fill the Uint8Array with data returned from getByteFrequencyData() 


A Uint8Array.


The following example shows basic usage of an AudioContext to create an AnalyserNode, then requestAnimationFrame and <canvas> to collect frequency data repeatedly and draw a "winamp bargraph style" output of the current audio input. For more examples/information, check out our Voice-change-O-matic demo (see app.js lines 128–205 for relevant code).

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
var analyser = audioCtx.createAnalyser();


analyser.fftSize = 256;
var bufferLength = analyser.frequencyBinCount;
var dataArray = new Uint8Array(bufferLength);

canvasCtx.clearRect(0, 0, WIDTH, HEIGHT);

function draw() {
  drawVisual = requestAnimationFrame(draw);


  canvasCtx.fillStyle = 'rgb(0, 0, 0)';
  canvasCtx.fillRect(0, 0, WIDTH, HEIGHT);

  var barWidth = (WIDTH / bufferLength) * 2.5;
  var barHeight;
  var x = 0;

  for(var i = 0; i < bufferLength; i++) {
    barHeight = dataArray[i];

    canvasCtx.fillStyle = 'rgb(' + (barHeight+100) + ',50,50)';

    x += barWidth + 1;



The Uint8Array that the frequency domain data will be copied to.


Specification Status Comment
Web Audio API
The definition of 'getByteFrequencyData()' in that specification.
Working Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 10.0webkit 25.0 (25.0)  No support 15.0webkit
22 (unprefixed)
Feature Android Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support ? 26.0 1.2 ? ? ? 33.0

See also

Document Tags and Contributors

 Last updated by: rolfedh,