Revision 719157 of AnalyserNode

<p>{{APIRef()}}</p>
<p>The <strong><code>AnalyserNode</code></strong><strong> </strong>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.</p>
<p>An <code>AnalyzerNode</code> has exactly one input and one output. The node works even if the output is not connected.</p>
<p><img alt="Without modifying the audio stream, the node allows to get the frequency and time-domain data associated to it, using a FFT." src="https://mdn.mozillademos.org/files/9707/WebAudioFFT.png" style="width: 661px; height: 174px;" /></p>
<ul class="audionodebox">
 <li><dfn>Number of inputs</dfn> <code>1</code></li>
 <li><dfn>Number of outputs</dfn> <code>1</code> (but may be left unconnected)</li>
 <li><dfn>Channel count mode</dfn> <code>"explicit"</code></li>
 <li><dfn>Channel count</dfn> <code>1</code></li>
 <li><dfn>Channel interpretation</dfn> <code>"speakers"</code></li>
</ul>
<div class="note">
 <p><strong>Note</strong>: See the guide <a href="/en-US/docs/Web/API/Web_Audio_API/Visualizations_with_Web_Audio_API">Visualizations with Web Audio API</a> for more information on creating audio visualizations.</p>
</div>
<h2 id="Properties">Properties</h2>
<p><em>Inherits properties from its parent, </em><em>{{domxref("AudioNode")}}</em>.</p>
<dl>
 <dt>
  <span id="cke_bm_91S" style="display: none;">&nbsp;</span>{{domxref("AnalyserNode.fftSize")}}</dt>
 <dd>
  Is an unsigned long value representing the size of the FFT (<a href="https://en.wikipedia.org/wiki/Fast_Fourier_transform" title="/en-US/docs/">Fast Fourier Transform</a>) to be used to determine the frequency domain.</dd>
 <dt>
  {{domxref("AnalyserNode.frequencyBinCount")}} {{readonlyInline}}</dt>
 <dd>
  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.</dd>
 <dt>
  {{domxref("AnalyserNode.minDecibels")}}</dt>
 <dd>
  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 <code>getByteFrequencyData()</code>.</dd>
 <dt>
  {{domxref("AnalyserNode.maxDecibels")}}</dt>
 <dd>
  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 <code>getByteFrequencyData()</code>.</dd>
 <dt>
  {{domxref("AnalyserNode.smoothingTimeConstant")}}</dt>
 <dd>
  Is a double value representing the averaging constant with the last analysis frame — basically, it makes the transition between values over time smoother.</dd>
</dl>
<h2 id="Methods">Methods</h2>
<p><em>Inherits methods from its parent, </em><em>{{domxref("AudioNode")}}</em>.</p>
<dl>
 <dt>
  {{domxref("AnalyserNode.getFloatFrequencyData()")}}</dt>
 <dd>
  Copies the current frequency data into a {{domxref("Float32Array")}} array passed into it.</dd>
</dl>
<dl>
 <dt>
  {{domxref("AnalyserNode.getByteFrequencyData()")}}</dt>
 <dd>
  Copies the current frequency data into a {{domxref("Uint8Array")}} (unsigned byte array) passed into it.</dd>
</dl>
<dl>
 <dt>
  {{domxref("AnalyserNode.getFloatTimeDomainData()")}}</dt>
 <dd>
  Copies the current waveform, or time-domain, data into a {{domxref("Float32Array")}} array passed into it.</dd>
 <dt>
  {{domxref("AnalyserNode.getByteTimeDomainData()")}}</dt>
 <dd>
  Copies the current waveform, or time-domain, data into a {{domxref("Uint8Array")}} (unsigned byte array) passed into it.</dd>
</dl>
<h2 id="Example">Example</h2>
<p>The following example shows basic usage of an {{domxref("AudioContext")}} to create an <code>AnalyserNode</code>, 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 <a href="https://mdn.github.io/voice-change-o-matic/">Voice-change-O-matic</a> demo (see <a href="https://github.com/mdn/voice-change-o-matic/blob/gh-pages/scripts/app.js#L128-L205">app.js lines 128–205</a> for relevant code).</p>
<pre class="brush: js">
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);

// draw an oscilloscope of the current audio source

function draw() {

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; drawVisual = requestAnimationFrame(draw);

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; analyser.getByteTimeDomainData(dataArray);

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; canvasCtx.fillStyle = 'rgb(200, 200, 200)';
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; canvasCtx.fillRect(0, 0, WIDTH, HEIGHT);

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; canvasCtx.lineWidth = 2;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; canvasCtx.strokeStyle = 'rgb(0, 0, 0)';

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; canvasCtx.beginPath();

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; var sliceWidth = WIDTH * 1.0 / bufferLength;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; var x = 0;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; for(var i = 0; i &lt; bufferLength; i++) {
&nbsp; &nbsp;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; var v = dataArray[i] / 128.0;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; var y = v * HEIGHT/2;

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

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; x += sliceWidth;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }

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

&nbsp;&nbsp;&nbsp; draw();</pre>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('Web Audio API', '#the-analysernode-interface', 'AnalyserNode')}}</td>
   <td>{{Spec2('Web Audio API')}}</td>
   <td>&nbsp;</td>
  </tr>
 </tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<div>
 {{CompatibilityTable}}</div>
<div id="compat-desktop">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Chrome</th>
    <th>Firefox (Gecko)</th>
    <th>Internet Explorer</th>
    <th>Opera</th>
    <th>Safari (WebKit)</th>
   </tr>
   <tr>
    <td>Basic support</td>
    <td>{{CompatChrome(10.0)}}{{property_prefix("webkit")}}</td>
    <td>{{CompatGeckoDesktop(25.0)}}&nbsp;</td>
    <td>{{CompatNo}}</td>
    <td>15.0{{property_prefix("webkit")}}<br />
     22 (unprefixed)</td>
    <td>6.0{{property_prefix("webkit")}}</td>
   </tr>
  </tbody>
 </table>
</div>
<div id="compat-mobile">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Android</th>
    <th>Firefox Mobile (Gecko)</th>
    <th>Firefox OS</th>
    <th>IE Mobile</th>
    <th>Opera Mobile</th>
    <th>Safari Mobile</th>
    <th>Chrome for Android</th>
   </tr>
   <tr>
    <td>Basic support</td>
    <td>{{CompatUnknown}}</td>
    <td>26.0</td>
    <td>1.2</td>
    <td>{{CompatUnknown}}</td>
    <td>{{CompatUnknown}}</td>
    <td>{{CompatUnknown}}</td>
    <td>33.0</td>
   </tr>
  </tbody>
 </table>
</div>
<h2 id="See_also">See also</h2>
<ul>
 <li><a href="/en-US/docs/Web_Audio_API/Using_Web_Audio_API">Using the Web Audio API</a></li>
</ul>