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AnalyserNode

files/en-us/web/api/analysernode/index.md

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{{APIRef("Web Audio API")}}

The AnalyserNode interface represents a node able to provide real-time frequency and time-domain analysis information. It is an {{domxref("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.

{{InheritanceDiagram}}

<table class="properties"> <tbody> <tr> <th scope="row">Number of inputs</th> <td><code>1</code></td> </tr> <tr> <th scope="row">Number of outputs</th> <td><code>1</code> (but may be left unconnected)</td> </tr> <tr> <th scope="row">Channel count mode</th> <td><code>"max"</code></td> </tr> <tr> <th scope="row">Channel count</th> <td><code>2</code></td> </tr> <tr> <th scope="row">Channel interpretation</th> <td><code>"speakers"</code></td> </tr> </tbody> </table>

Constructor

  • {{domxref("AnalyserNode.AnalyserNode", "AnalyserNode()")}}
    • : Creates a new instance of an AnalyserNode object.

Instance properties

Inherits properties from its parent, {{domxref("AudioNode")}}.

  • {{domxref("AnalyserNode.fftSize")}}
    • : An unsigned long value representing the size of the FFT (Fast Fourier Transform) to be used to determine the frequency domain.
  • {{domxref("AnalyserNode.frequencyBinCount")}} {{ReadOnlyInline}}
    • : 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.
  • {{domxref("AnalyserNode.minDecibels")}}
    • : 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().
  • {{domxref("AnalyserNode.maxDecibels")}}
    • : 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().
  • {{domxref("AnalyserNode.smoothingTimeConstant")}}
    • : A double value representing the averaging constant with the last analysis frame — basically, it makes the transition between values over time smoother.

Instance methods

Inherits methods from its parent, {{domxref("AudioNode")}}.

  • {{domxref("AnalyserNode.getFloatFrequencyData()")}}
    • : Copies the current frequency data into a {{jsxref("Float32Array")}} array passed into it.
  • {{domxref("AnalyserNode.getByteFrequencyData()")}}
    • : Copies the current frequency data into a {{jsxref("Uint8Array")}} (unsigned byte array) passed into it.
  • {{domxref("AnalyserNode.getFloatTimeDomainData()")}}
    • : Copies the current waveform, or time-domain, data into a {{jsxref("Float32Array")}} array passed into it.
  • {{domxref("AnalyserNode.getByteTimeDomainData()")}}
    • : Copies the current waveform, or time-domain, data into a {{jsxref("Uint8Array")}} (unsigned byte array) passed into it.

Examples

[!NOTE] See the guide Visualizations with Web Audio API for more information on creating audio visualizations.

Basic usage

The following example shows basic usage of an {{domxref("AudioContext")}} to create an AnalyserNode, then {{domxref("window.requestAnimationFrame()","requestAnimationFrame")}} and {{htmlelement("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 108-193 for relevant code).

js
const audioCtx = new AudioContext();

// …

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

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

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

// Get a canvas defined with ID "oscilloscope"
const canvas = document.getElementById("oscilloscope");
const 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();

  const sliceWidth = (canvas.width * 1.0) / bufferLength;
  let x = 0;

  for (let i = 0; i < bufferLength; i++) {
    const v = dataArray[i] / 128.0;
    const 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();

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

See also