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AnalyserNode.getFloatFrequencyData

The getFloatFrequencyData() method of the AnalyserNode Interface copies the current frequency data into a Float32Array array passed into it.

If you need higher performance and don't care about precision, you can use AnalyserNode.getByteFrequencyData() instead, which works on a Uint8Array.

Syntax

void analyser.getFloatFrequencyData(array);

Parameters

array: The Float32Array that 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 the AnalyserNode.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

Feature	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	14	Yes	25	No	15	6

Feature	Android webview	Chrome for Android	Edge mobile	Firefox for Android	IE mobile	Opera Android	iOS Safari
Basic support	Yes	14	Yes	26	No	15	?