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Showing content from http://developer.mozilla.org/en-US/docs/Web/API/AnalyserNode/getByteTimeDomainData below:

AnalyserNode: getByteTimeDomainData() method - Web APIs

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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.

getByteTimeDomainData(array)

array

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

None (undefined).

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).

const audioCtx = new AudioContext();
const analyser = audioCtx.createAnalyser();

// …

analyser.fftSize = 2048;
const bufferLength = analyser.fftSize;
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)";

  const sliceWidth = (WIDTH * 1.0) / bufferLength;
  let x = 0;

  canvasCtx.beginPath();
  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(WIDTH, HEIGHT / 2);
  canvasCtx.stroke();
}

draw();

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