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index.md
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---
title: "AnalyserNode: fftSize property"
short-title: fftSize
slug: Web/API/AnalyserNode/fftSize
page-type: web-api-instance-property
browser-compat: api.AnalyserNode.fftSize
---
{{APIRef("Web Audio API")}}
The **`fftSize`** property of the {{domxref("AnalyserNode")}} interface is an unsigned long value and represents the window size in samples that is used when performing a [Fast Fourier Transform](https://en.wikipedia.org/wiki/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` {{domxref("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 {{domxref("AudioContext")}} to create an `AnalyserNode`, then {{domxref("window.requestAnimationFrame()","requestAnimationFrame")}} and {{htmlelement("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](https://github.com/mdn/webaudio-examples/tree/main/voice-change-o-matic) demo (see [app.js lines 108–193](https://github.com/mdn/webaudio-examples/blob/main/voice-change-o-matic/scripts/app.js#L108-L193) 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
{{Specifications}}
## Browser compatibility
{{Compat}}
## See also
- [Using the Web Audio API](/en-US/docs/Web/API/Web_Audio_API/Using_Web_Audio_API)