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AnalyserNode: getFloatTimeDomainData() method

The getFloatTimeDomainData() method of the AnalyserNode Interface copies the current waveform, or time-domain, data into a Float32Array array passed into it. Each array value is a sample, the magnitude of the signal at a particular time.

Syntax

getFloatTimeDomainData(array)

Parameters

array: The Float32Array 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.

Return value

None (undefined).

Examples

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 (window.AudioContext || window.webkitAudioContext)();
const analyser = audioCtx.createAnalyser();

// …

analyser.fftSize = 1024;
const bufferLength = analyser.fftSize;
console.log(bufferLength);
const dataArray = new Float32Array(bufferLength);

canvasCtx.clearRect(0, 0, WIDTH, HEIGHT);

function draw() {
  drawVisual = requestAnimationFrame(draw);
  analyser.getFloatTimeDomainData(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] * 200.0;
    const y = HEIGHT / 2 + v;

    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
Web Audio API # dom-analysernode-getfloattimedomaindata

Browser compatibility