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AnalyserNode.getByteFrequencyData

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.

Syntax

var audioCtx = new AudioContext();
var analyser = audioCtx.createAnalyser();
var dataArray = new Uint8Array(analyser.frequencyBinCount); // Uint8Array should be the same length as the frequencyBinCount 

void analyser.getByteFrequencyData(dataArray); // fill the Uint8Array with data returned from getByteFrequencyData() 

Parameters

array
The Uint8Array that the frequency domain data will be copied to. For any sample which is silent, the value is -Infinity.
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.

Return value

None.

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 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;
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;
  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 + 1;
  }
};

draw();

Parameters

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

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 14 12 25 No 15 6
Mobile
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

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode/getByteFrequencyData