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 ⁨July 2015⁩.

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.

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();