AnalyserNode: frequencyBinCount property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since April 2021.

The frequencyBinCount read-only property of the AnalyserNode interface contains the total number of data points available to AudioContext sampleRate. This is half of the value of the AnalyserNode.fftSize. The two methods' indices have a linear relationship with the frequencies they represent, between 0 and the Nyquist frequency.

Value

An unsigned integer, equal to the number of values that AnalyserNode.getByteFrequencyData() and AnalyserNode.getFloatFrequencyData() copy into the provided TypedArray.

For technical reasons related to how the Fast Fourier transform is defined, it is always half the value of AnalyserNode.fftSize. Therefore, it will be one of 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, and 16384.

Examples

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 bar graph style" output of the current audio input. For more complete applied examples/information, check out our Voice-change-O-matic demo.

js
const audioCtx = new AudioContext();
const analyser = audioCtx.createAnalyser();
analyser.minDecibels = -90;
analyser.maxDecibels = -10;

// …

analyser.fftSize = 256;
const bufferLength = analyser.frequencyBinCount;
console.log(bufferLength);
const 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);

  const barWidth = (WIDTH / bufferLength) * 2.5 - 1;
  let barHeight;
  let x = 0;

  for (let 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;
  }
}

draw();

Specifications

Specification
Web Audio API
# dom-analysernode-frequencybincount

Browser compatibility

See also