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.

Syntax

``````var curValue = analyserNode.fftSize;
analyserNode.fftSize = newValue;
``````

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`.

Note: If its value is not a power of 2, or it is outside the specified range, a `DOMException` with the name `IndexSizeError` is thrown.

Example

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 Status Comment
Web Audio API
The definition of 'fftSize' in that specification.
Working Draft

Browser compatibility

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