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 252^5 and 2152^15, 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.fftSize;
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

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome Full support 14Edge Full support 12Firefox Full support 25IE No support NoOpera Full support 15Safari Full support 6WebView Android Full support YesChrome Android Full support 18Edge Mobile Full support YesFirefox Android Full support 26Opera Android Full support 15Safari iOS ? Samsung Internet Android Full support Yes

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown

See also

Document Tags and Contributors

Last updated by: Jedipedia,