AnalyserNode

The AnalyserNode interface represents a node able to provide real-time frequency and time-domain analysis information. It is an AudioNode that passes the audio stream unchanged from the input to the output, but allows you to take the generated data, process it, and create audio visualizations.

An AnalyserNode has exactly one input and one output. The node works even if the output is not connected.

AnalyserNode()

Creates a new instance of an AnalyserNode object.

Inherits properties from its parent, AudioNode.

AnalyserNode.fftSize

Is an unsigned long value representing the size of the FFT (Fast Fourier Transform) to be used to determine the frequency domain.

AnalyserNode.frequencyBinCount Read only

Is an unsigned long value half that of the FFT size. This generally equates to the number of data values you will have to play with for the visualization.

AnalyserNode.minDecibels

Is a double value representing the minimum power value in the scaling range for the FFT analysis data, for conversion to unsigned byte values — basically, this specifies the minimum value for the range of results when using getByteFrequencyData().

AnalyserNode.maxDecibels

Is a double value representing the maximum power value in the scaling range for the FFT analysis data, for conversion to unsigned byte values — basically, this specifies the maximum value for the range of results when using getByteFrequencyData().

AnalyserNode.smoothingTimeConstant

Is a double value representing the averaging constant with the last analysis frame — basically, it makes the transition between values over time smoother.

Inherits methods from its parent, AudioNode.

AnalyserNode.getFloatFrequencyData()

Copies the current frequency data into a Float32Array array passed into it.

AnalyserNode.getByteFrequencyData()

Copies the current frequency data into a Uint8Array (unsigned byte array) passed into it.

AnalyserNode.getFloatTimeDomainData()

Copies the current waveform, or time-domain, data into a Float32Array array passed into it.

AnalyserNode.getByteTimeDomainData()

Copies the current waveform, or time-domain, data into a Uint8Array (unsigned byte array) passed into it.

The following example shows basic usage of an AudioContext to create an AnalyserNode, then requestAnimationFrame and <canvas> to collect time domain data repeatedly and draw an "oscilloscope style" output of the current audio input. For more complete applied examples/information, check out our Voice-change-O-matic demo (see app.js lines 128–205 for relevant code).

var audioCtx = new(window.AudioContext || window.webkitAudioContext)();

// ...

var analyser = audioCtx.createAnalyser();
analyser.fftSize = 2048;

var bufferLength = analyser.frequencyBinCount;
var dataArray = new Uint8Array(bufferLength);
analyser.getByteTimeDomainData(dataArray);

// Connect the source to be analysed
source.connect(analyser);

// Get a canvas defined with ID "oscilloscope"
var canvas = document.getElementById("oscilloscope");
var canvasCtx = canvas.getContext("2d");

// draw an oscilloscope of the current audio source

function draw() {

  requestAnimationFrame(draw);

  analyser.getByteTimeDomainData(dataArray);

  canvasCtx.fillStyle = "rgb(200, 200, 200)";
  canvasCtx.fillRect(0, 0, canvas.width, canvas.height);

  canvasCtx.lineWidth = 2;
  canvasCtx.strokeStyle = "rgb(0, 0, 0)";

  canvasCtx.beginPath();

  var sliceWidth = canvas.width * 1.0 / bufferLength;
  var x = 0;

  for (var i = 0; i < bufferLength; i++) {

    var v = dataArray[i] / 128.0;
    var y = v * canvas.height / 2;

    if (i === 0) {
      canvasCtx.moveTo(x, y);
    } else {
      canvasCtx.lineTo(x, y);
    }

    x += sliceWidth;
  }

  canvasCtx.lineTo(canvas.width, canvas.height / 2);
  canvasCtx.stroke();
}

draw();

• Using the Web Audio API