The maxDecibels property of the AnalyserNode interface is a double value representing the maximum power value in the scaling range for the FFT analysis data, for conversion to unsigned byte values — basically, this specifies the maximum value for the range of results when using getByteFrequencyData().


var curValue = analyserNode.maxDecibels;
analyserNode.maxDecibels = newValue;


A double, representing the maximum decibel value for scaling the FFT analysis data, where 0 dB is the loudest possible sound, -10 dB is a 10th of that, etc. The default value is -30 dB.

When getting data from getByteFrequencyData(), any frequencies with an amplitude of maxDecibels or higher will be returned as 255.

Note: If a value less than or equal to AnalyserNode.minDecibels is set, an IndexSizeError 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).

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


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;



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

Browser compatibility

BCD tables only load in the browser

See also