AnalyserNode: smoothingTimeConstant property
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 (window.AudioContext || window.webkitAudioContext)();
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
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