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()
.
Syntax
var curValue = analyserNode.minDecibels;
analyserNode.minDecibels = newValue;
Value
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.
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 [[../../../../../../../mdn.github.io/voice-change-o-matic/index|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 APIThe definition of 'minDecibels' in that specification. | Working Draft |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
minDecibels
|
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
See also
AnalyserNode.minDecibels by Mozilla Contributors is licensed under CC-BY-SA 2.5.