AnalyserNode.frequencyBinCount
The frequencyBinCount
read-only property of the AnalyserNode
interface is an unsigned integer half that of the AnalyserNode.fftSize
. This generally equates to the number of data values you will have to play with for the visualization.
Value
An unsigned integer, equal to the number of values that AnalyserNode.getByteFrequencyData()
and AnalyserNode.getFloatFrequencyData()
copy into the provided TypedArray
.
For technical reasons related to how the Fast Fourier transform is defined, it is always half the value of AnalyserNode.fftSize
. Therefore, it will be one of 16
, 32
, 64
, 128
, 256
, 512
, 1024
, 2048
, 4096
, 8192
, and 16384
.
Examples
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 - 1;
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;
}
};
draw();
Specifications
Specification |
---|
Web Audio API # dom-analysernode-frequencybincount |
Browser compatibility
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