The smoothingTimeConstant property of the AnalyserNode interface is a double value representing the averaging constant with the last analysis frame. It's basically an average between the current buffer and the last buffer the AnalyserNode processed, and results in a much smoother set of value changes over time.


var smoothValue = analyserNode.smoothingTimeConstant;
analyserNode.smoothingTimeConstant = newValue;


A double within the range 0 to 1 (0 meaning no time averaging). The default value is 0.8.

If 0 is set, there is no averaging done, whereas a value of 1 means "overlap the previous and current buffer quite a lot while computing the value", which essentially smoothes the changes across AnalyserNode.getFloatFrequencyData/AnalyserNode.getByteFrequencyData calls.

In technical terms, we apply a Blackman window and smooth the values over time. The default value is good enough for most cases.

Note: If a value outside the range 0–1 is set, an INDEX_SIZE_ERR exception is thrown.


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 demo (see app.js lines 128–205 for relevant code).

If you are curious about the effect the smoothingTimeConstant() has, try cloning the above example and setting analyser.smoothingTimeConstant = 0; instead. You'll notice that the value changes are much more jarring.

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
var analyser = audioCtx.createAnalyser();
analyser.minDecibels = -90;
analyser.maxDecibels = -10;
analyser.smoothingTimeConstant = 0.85;


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;



Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 14 12 25 No 15 6
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support Yes 18 Yes 26 15 ? Yes

See also

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