AnalyserNode: fftSize property
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 amplitude 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 108–193 for relevant code).
js
const audioCtx = new (window.AudioContext || window.webkitAudioContext)();
const analyser = audioCtx.createAnalyser();
// …
analyser.fftSize = 2048;
const bufferLength = analyser.frequencyBinCount;
const 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();
const sliceWidth = (WIDTH * 1.0) / bufferLength;
let x = 0;
for (let i = 0; i < bufferLength; i++) {
const v = dataArray[i] / 128.0;
const 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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