The getByteFrequencyData()
method of the AnalyserNode
interface copies the current frequency data into a Uint8Array
(unsigned byte array) passed into it.
The frequency data is composed of integers on a scale from 0 to 255.
Each item in the array represents the decibel value for a specific frequency. The frequencies are spread linearly from 0 to 1/2 of the sample rate. For example, for 48000
sample rate, the last item of the array will represent the decibel value for 24000
Hz.
If the array has fewer elements than the AnalyserNode.frequencyBinCount
, excess elements are dropped. If it has more elements than needed, excess elements are ignored.
getByteFrequencyData(array)
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 bargraph style" output of the current audio input. For more examples/information, check out our Voice-change-O-matic demo (see app.js lines 128–205 for relevant code).
var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
var analyser = audioCtx.createAnalyser();
...
analyser.fftSize = 256;
var bufferLength = analyser.frequencyBinCount;
console.log(bufferLength);
var 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);
var barWidth = (WIDTH / bufferLength) * 2.5;
var barHeight;
var x = 0;
for(var 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();