AnalyserNode.fftSize
The fftSize
property of the AnalyserNode
interface is an unsigned long value and represents the window size in samples that is used when performing a Fast Fourier Transform (FFT) to get frequency domain data.
Value
An unsigned integer, representing the window size of the FFT, given in number of samples. A higher value will result in more details in the frequency domain but fewer details in the time domain.
Must be a power of 2 between 2^5 and 2^15, so one of: 32
, 64
, 128
, 256
, 512
, 1024
, 2048
, 4096
, 8192
, 16384
, and 32768
. Defaults to 2048
.
Exceptions
IndexSizeError
DOMException
-
Thrown if the value set is not a power of 2, or is outside the allowed range.
Examples
The following example shows basic usage of an AudioContext
to create an AnalyserNode
, then requestAnimationFrame
and <canvas>
to collect time domain data repeatedly and draw an "oscilloscope 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.fftSize = 2048;
var bufferLength = analyser.frequencyBinCount;
var dataArray = new Uint8Array(bufferLength);
analyser.getByteTimeDomainData(dataArray);
// draw an oscilloscope of the current audio source
function draw() {
drawVisual = requestAnimationFrame(draw);
analyser.getByteTimeDomainData(dataArray);
canvasCtx.fillStyle = 'rgb(200, 200, 200)';
canvasCtx.fillRect(0, 0, WIDTH, HEIGHT);
canvasCtx.lineWidth = 2;
canvasCtx.strokeStyle = 'rgb(0, 0, 0)';
canvasCtx.beginPath();
var sliceWidth = WIDTH * 1.0 / bufferLength;
var x = 0;
for(var i = 0; i < bufferLength; i++) {
var v = dataArray[i] / 128.0;
var y = v * HEIGHT/2;
if(i === 0) {
canvasCtx.moveTo(x, y);
} else {
canvasCtx.lineTo(x, y);
}
x += sliceWidth;
}
canvasCtx.lineTo(canvas.width, canvas.height/2);
canvasCtx.stroke();
};
draw();
Specifications
Specification |
---|
Web Audio API # dom-analysernode-fftsize |
Browser compatibility
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