AnalyserNode: maxDecibels property
The maxDecibels
property of the AnalyserNode
interface is a double value representing the maximum power value in the scaling range for the FFT analysis data, for conversion to unsigned byte values — basically, this specifies the maximum value for the range of results when using getByteFrequencyData()
.
Value
A double, representing the maximum decibel value for scaling the FFT analysis data, where 0
dB is the loudest possible sound, -10
dB is a 10th of that, etc. The default value is -30
dB.
When getting data from getByteFrequencyData()
, any frequencies with an amplitude of maxDecibels
or higher will be returned as 255
.
Exceptions
IndexSizeError
DOMException
-
Thrown if a value less than or equal to
AnalyserNode.minDecibels
is set.
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).
js
const audioCtx = new (window.AudioContext || window.webkitAudioContext)();
const analyser = audioCtx.createAnalyser();
analyser.minDecibels = -90;
analyser.maxDecibels = -10;
// …
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-maxdecibels |
Browser compatibility
BCD tables only load in the browser