AnalyserNode.getFloatFrequencyData() - Web APIs 编辑
The getFloatFrequencyData() method of the AnalyserNode Interface copies the current frequency data into a Float32Array array passed into it.
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 you need higher performance and don't care about precision, you can use AnalyserNode.getByteFrequencyData() instead, which works on a Uint8Array.
Syntax
var audioCtx = new AudioContext(); var analyser = audioCtx.createAnalyser(); var dataArray = new Float32Array(analyser.frequencyBinCount); // Float32Array should be the same length as the frequencyBinCount void analyser.getFloatFrequencyData(dataArray); // fill the Float32Array with data returned from getFloatFrequencyData()
Parameters
array- The
Float32Arraythat the frequency domain data will be copied to. For any sample which is silent, the value is-Infinity.
If the array has fewer elements than theAnalyserNode.frequencyBinCount, excess elements are dropped. If it has more elements than needed, excess elements are ignored.
Return value
None.
Example
const audioCtx = new AudioContext();
const analyser = audioCtx.createAnalyser();
// Float32Array should be the same length as the frequencyBinCount
const myDataArray = new Float32Array(analyser.frequencyBinCount);
// fill the Float32Array with data returned from getFloatFrequencyData()
analyser.getFloatFrequencyData(myDataArray);
Drawing a spectrum
The following example shows basic usage of an AudioContext to connect a MediaElementAudioSourceNode to an AnalyserNode. While the audio is playing, we collect the frequency data repeatedly with requestAnimationFrame() and draw a "winamp bargraph style" to a <canvas> element.
For more complete applied examples/information, check out our Voice-change-O-matic-float-data demo (see the source code too).
<!doctype html>
<body>
<script>
const audioCtx = new AudioContext();
//Create audio source
//Here, we use an audio file, but this could also be e.g. microphone input
const audioEle = new Audio();
audioEle.src = 'my-audio.mp3';//insert file name here
audioEle.autoplay = true;
audioEle.preload = 'auto';
const audioSourceNode = audioCtx.createMediaElementSource(audioEle);
//Create analyser node
const analyserNode = audioCtx.createAnalyser();
analyserNode.fftSize = 256;
const bufferLength = analyserNode.frequencyBinCount;
const dataArray = new Float32Array(bufferLength);
//Set up audio node network
audioSourceNode.connect(analyserNode);
analyserNode.connect(audioCtx.destination);
//Create 2D canvas
const canvas = document.createElement('canvas');
canvas.style.position = 'absolute';
canvas.style.top = 0;
canvas.style.left = 0;
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
document.body.appendChild(canvas);
const canvasCtx = canvas.getContext('2d');
canvasCtx.clearRect(0, 0, canvas.width, canvas.height);
function draw() {
//Schedule next redraw
requestAnimationFrame(draw);
//Get spectrum data
analyserNode.getFloatFrequencyData(dataArray);
//Draw black background
canvasCtx.fillStyle = 'rgb(0, 0, 0)';
canvasCtx.fillRect(0, 0, canvas.width, canvas.height);
//Draw spectrum
const barWidth = (canvas.width / bufferLength) * 2.5;
let posX = 0;
for (let i = 0; i < bufferLength; i++) {
const barHeight = (dataArray[i] + 140) * 2;
canvasCtx.fillStyle = 'rgb(' + Math.floor(barHeight + 100) + ', 50, 50)';
canvasCtx.fillRect(posX, canvas.height - barHeight / 2, barWidth, barHeight / 2);
posX += barWidth + 1;
}
};
draw();
</script>
</body>Specifications
| Specification | Status | Comment |
|---|---|---|
| Web Audio API The definition of 'getFloatFrequencyData()' in that specification. | Working Draft |
Browser compatibility
BCD tables only load in the browser
See also
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