AnalyserNode.frequencyBinCount

The frequencyBinCount read-only property of the AnalyserNode interface is an unsigned integer half that of the AnalyserNode.fftSize. This generally equates to the number of data values you will have to play with for the visualization.

Syntax

var arrayLength = analyserNode.frequencyBinCount;

Value

An unsigned integer, equal to the number of values that AnalyserNode.getByteFrequencyData() and AnalyserNode.getFloatFrequencyData() copy into the provided TypedArray.

For technical reasons related to how the Fast Fourier transform is defined, it is always half the value of AnalyserNode.fftSize. Therefore, it will be one of 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, and 16384.

Example

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).

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

  ...

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

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

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

  analyser.getByteFrequencyData(dataArray);

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

  var barWidth = (WIDTH / bufferLength) * 2.5 - 1;
  var barHeight;
  var x = 0;

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

    canvasCtx.fillStyle = 'rgb(' + (barHeight+100) + ',50,50)';
    canvasCtx.fillRect(x,HEIGHT-barHeight/2,barWidth,barHeight/2);

    x += barWidth;
  }
};

draw();

Specifications

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
frequencyBinCount
14
12
25
No
15
6
≤37
18
25
14
6
1.0

See also

© 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode/frequencyBinCount