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


var curValue = analyserNode.minDecibels;
analyserNode.minDecibels = newValue;


A double, representing the minimum 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 -100 dB.

When getting data from getFloatFrequencyData() or getByteFrequencyData(), any frequencies with an amplitude of minDecibels or lower will be returned as 0.0 or 0, respectively.

Note: If a value greater than AnalyserNode.maxDecibels 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).

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 'minDecibels' in that specification.
Working Draft

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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