files/en-us/web/api/analysernode/getfloatfrequencydata/index.md
{{ APIRef("Web Audio API") }}
The getFloatFrequencyData() method of the {{domxref("AnalyserNode")}} Interface copies the current frequency data into a {{jsxref("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 a 48000 Hz 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 {{domxref("AnalyserNode.getByteFrequencyData()")}} instead, which works on a {{jsxref("Uint8Array")}}.
getFloatFrequencyData(array)
array
-Infinity.
If the array has fewer elements than the {{domxref("AnalyserNode.frequencyBinCount")}}, excess elements are dropped. If it has more elements than needed, excess elements are ignored.None ({{jsxref("undefined")}}).
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);
The following example shows basic usage of an {{domxref("AudioContext")}} to connect a {{domxref("MediaElementAudioSourceNode")}} to an AnalyserNode. While the audio is playing, we collect the frequency data repeatedly with {{domxref("window.requestAnimationFrame()","requestAnimationFrame()")}} and draw a "winamp bar graph style" to a {{htmlelement("canvas")}} element.
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();
// 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();
{{Specifications}}
{{Compat}}