The getFloatFrequencyData() method of the AnalyserNode Interface copies the current frequency data into a Float32Array 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 myDataArray = new Float32Array(analyser.frequencyBinCount); // Float32Array should be the same length as the frequencyBinCount 
analyser.getFloatFrequencyData(myDataArray); // fill the Float32Array with data returned from getFloatFrequencyData() 


A Float32Array.


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 complete applied examples/information, check out our Voice-change-O-matic-float-data demo (see the source code too).

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


analyser.fftSize = 256;
var bufferLength = analyser.frequencyBinCount;
var dataArray = new Float32Array(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] + 140)*2;
    canvasCtx.fillStyle = 'rgb(' + Math.floor(barHeight+100) + ',50,50)';
    x += barWidth + 1;



The Float32Array that the frequency domain data will be copied to.


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

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 10.0webkit 25.0 (25.0)  Not supported 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

 Contributors to this page: teoli, Fournux, chrisdavidmills
 Last updated by: teoli,