AnalyserNode: minDecibels 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 minDecibels property of the AnalyserNode interface is a double value representing the minimum power value in the scaling range for the FFT analysis data, for conversion to unsigned byte values — basically, this specifies the minimum value for the range of results when using getByteFrequencyData().
Value
A double, representing the minimum 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 -100 dB.
When getting data from getByteFrequencyData(), any frequencies with an amplitude of minDecibels or lower will be returned as 0.
Note:
If a value greater than AnalyserNode.maxDecibels 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).
const audioCtx = new AudioContext();
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
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| Web Audio API # dom-analysernode-mindecibels |
Browser compatibility
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minDecibels
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