AnalyserNode: smoothingTimeConstant property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since April 2021.

The smoothingTimeConstant property of the AnalyserNode interface is a double value representing the averaging constant with the last analysis frame. It's basically an average between the current buffer and the last buffer the AnalyserNode processed, and results in a much smoother set of value changes over time.

Value

A double within the range 0 to 1 (0 meaning no time averaging). The default value is 0.8.

If 0 is set, there is no averaging done, whereas a value of 1 means "overlap the previous and current buffer quite a lot while computing the value", which essentially smooths the changes across AnalyserNode.getFloatFrequencyData/AnalyserNode.getByteFrequencyData calls.

In technical terms, we apply a Blackman window and smooth the values over time. The default value is good enough for most cases.

Note: If a value outside the range 0–1 is set, an INDEX_SIZE_ERR exception is thrown.

Examples

The following example shows basic usage of an AudioContext to create an AnalyserNode, then requestAnimationFrame and <canvas> to collect frequency data repeatedly and draw a "winamp bar graph 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).

If you are curious about the effect the smoothingTimeConstant() has, try cloning the above example and setting analyser.smoothingTimeConstant = 0; instead. You'll notice that the value changes are much more jarring.

js
const audioCtx = new AudioContext();
const analyser = audioCtx.createAnalyser();
analyser.minDecibels = -90;
analyser.maxDecibels = -10;
analyser.smoothingTimeConstant = 0.85;

// …

analyser.fftSize = 256;
const bufferLength = analyser.frequencyBinCount;
console.log(bufferLength);
const dataArray = new Uint8Array(bufferLength);

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

function draw() {
  drawVisual = requestAnimationFrame(draw);

  analyser.getByteFrequencyData(dataArray);

  canvasCtx.fillStyle = "rgb(0 0 0)";
  canvasCtx.fillRect(0, 0, WIDTH, HEIGHT);

  const barWidth = (WIDTH / bufferLength) * 2.5;
  let barHeight;
  let x = 0;

  for (let i = 0; i < bufferLength; i++) {
    barHeight = dataArray[i];

    canvasCtx.fillStyle = `rgb(${barHeight + 100} 50 50)`;
    canvasCtx.fillRect(x, HEIGHT - barHeight / 2, barWidth, barHeight / 2);

    x += barWidth + 1;
  }
}

draw();

Specifications

Specification
Web Audio API
# dom-analysernode-smoothingtimeconstant

Browser compatibility

BCD tables only load in the browser

See also