AnalyserNode.getByteTimeDomainData

The getByteTimeDomainData() method of the AnalyserNode Interface copies the current waveform, or time-domain, data into a Uint8Array (unsigned byte array) passed into it.

If the array has fewer elements than the AnalyserNode.fftSize, excess elements are dropped. If it has more elements than needed, excess elements are ignored.

Syntax

var audioCtx = new AudioContext();
var analyser = audioCtx.createAnalyser();
var dataArray = new Uint8Array(analyser.fftSize); // Uint8Array should be the same length as the fftSize 
analyser.getByteTimeDomainData(dataArray); // fill the Uint8Array with data returned from getByteTimeDomainData() 

Returns

A Uint8Array.

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();

Parameters

array

The Uint8Array that the time domain data will be copied to.

Specifications

Browser compatibility

See also

• Using the Web Audio API