AnalyserNode: smoothingTimeConstant property

The smoothingTimeConstant property of the {{ domxref("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 {{domxref("AnalyserNode.getFloatFrequencyData")}}/{{domxref("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 {{domxref("AudioContext")}} to create an AnalyserNode, then {{domxref("window.requestAnimationFrame()","requestAnimationFrame")}} and {{htmlelement("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.

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();

Value

Examples

Specifications

Browser compatibility

See also