AnalyserNode: getFloatFrequencyData() method

The getFloatFrequencyData() method of the AnalyserNode Interface copies the current frequency data into a Float32Array array passed into it. Each array value is a sample, the magnitude of the signal at a particular time.

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 AnalyserNode.getByteFrequencyData() instead, which works on a Uint8Array.

Syntax

js

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 (undefined).

Examples

js

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 bar graph style" to a <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).

html

<!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
Web Audio API
# dom-analysernode-getfloatfrequencydata

Browser compatibility

BCD tables only load in the browser

See also