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/float values — basically, this specifies the maximum value for the range of results when using getFloatFrequencyData()
or getByteFrequencyData()
.
Syntax
var curValue = analyserNode.maxDecibels; analyserNode.maxDecibels = newValue;
Value
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 getFloatFrequencyData()
or getByteFrequencyData()
, any frequencies with an amplitude of maxDecibels
or higher will be returned as +1.0
or 255
, respectively.
Note: If a value less than or equal to AnalyserNode.minDecibels
is set, an IndexSizeError
exception is thrown.
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; 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();
Specifications
Specification | Status | Comment |
---|---|---|
Web Audio API The definition of 'maxDecibels' in that specification. |
Working Draft |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
maxDecibels | Chrome Full support 14 | Edge Full support 12 | Firefox Full support 25 | IE No support No | Opera Full support 15 | Safari Full support 6 | WebView Android Full support Yes | Chrome Android Full support 18 | Firefox Android Full support 26 | Opera Android Full support 14 | Safari iOS Full support 6 | Samsung Internet Android Full support 1.0 |
Legend
- Full support
- Full support
- No support
- No support