Revision 663753 of DynamicsCompressorNode

<p>{{ APIRef() }}</p>
<div>
 <p>The <code>DynamicsCompressorNode</code> interface provides a compression effect, which lowers the volume of the loudest parts of the signal in order to help prevent clipping and distortion that can occur when multiple sounds are played and multiplexed together at once. This is often used in musical production and game audio. <code>DynamicsCompressorNode</code> is an {{domxref("AudioNode")}} that has exactly one input and one output; it is created using the {{domxref("AudioContext.createDynamicsCompressor")}} method.</p>
</div>
<ul class="audionodebox">
 <li><dfn>Number of inputs</dfn> <code>1</code></li>
 <li><dfn>Number of outputs</dfn> <code>1</code></li>
 <li><dfn>Channel count mode</dfn> <code>"explicit"</code></li>
 <li><dfn>Channel count</dfn> <code>2</code></li>
 <li><dfn>Channel interpretation</dfn> <code>"speakers"</code></li>
</ul>
<h2 id="Properties">Properties</h2>
<p><em>Inherits properties from its parent, </em><em>{{domxref("AudioNode")}}</em>.</p>
<dl>
 <dt>
  {{domxref("DynamicsCompressorNode.threshold")}}</dt>
 <dd>
  <table class="withoutBorder">
   <tbody>
    <tr>
     <td><img alt="The threshold attribute has no effect on signals lowers than its value, but induce volume reduction on signal stronger than its value." src="https://mdn.mozillademos.org/files/5111/WebAudioThreshold.png" style="width: 257px; height: 219px; float: left;" /></td>
     <td style="vertical-align:top">Is a {{k-rate}} {{domxref("AudioParam")}} representing the decibel value above which the compression will start taking effect. Its default value is <code>-24</code> and it can be set between <code>-100</code> and <code>0</code>. (Though the <code>AudioParam</code> returned is read-only, the value it represents is not.)</td>
    </tr>
   </tbody>
  </table>
 </dd>
 <dt>
  {{domxref("DynamicsCompressorNode.knee")}}</dt>
 <dd>
  <table class="withoutBorder">
   <tbody>
    <tr>
     <td><img alt="Describes the effect of a knee, showing two curves one for a hard knee, the other for a soft knee." src="https://mdn.mozillademos.org/files/5113/WebAudioKnee.png" style="width: 257px; height: 244px;" /></td>
     <td style="vertical-align:top">Is a {{k-rate}} {{domxref("AudioParam")}} containing a decibel value representing the range above the threshold where the curve smoothly transitions to the compressed portion. Its default value is <code>30</code> and it can be set between <code>0</code> and <code>40</code>. (Though the <code>AudioParam</code> returned is read-only, the value it represents is not.)</td>
    </tr>
   </tbody>
  </table>
 </dd>
 <dt>
  {{domxref("DynamicsCompressorNode.ratio")}}</dt>
 <dd>
  <table class="withoutBorder">
   <tbody>
    <tr>
     <td><img alt="Describes the effect of different ratio on the output signal" src="https://mdn.mozillademos.org/files/5115/WebAudioRatio.png" /></td>
     <td style="vertical-align:top">Is a {{k-rate}} {{domxref("AudioParam")}} representing the amount of change, in dB, needed in the input for a 1 dB change in the output. Its default value is <code>12</code> and it can be set between <code>1</code> and <code>20</code>. (Though the <code>AudioParam</code> returned is read-only, the value it represents is not.)</td>
    </tr>
   </tbody>
  </table>
 </dd>
 <dt>
  {{domxref("DynamicsCompressorNode.reduction")}}</dt>
 <dd>
  Is a {{k-rate}} {{domxref("AudioParam")}} representing the amount of gain reduction currently applied by the compressor to the signal. Intended for metering purposes, it returns a value in dB, or <code>0</code> (no gain reduction) if no signal is fed into the <code>DynamicsCompressorNode</code>. The range of this value is between <code>-20</code> and <code>0</code> (in dB). (Though the <code>AudioParam</code> returned is read-only, the value it represents is not.)</dd>
 <dt>
  {{domxref("DynamicsCompressorNode.attack")}}</dt>
 <dd>
  Is a {{k-rate}} {{domxref("AudioParam")}} representing the amount of time, in seconds, required to reduce the gain by 10 dB. It defines how quick the signal is adapted when its volume is increased. Its default value is <code>0.003</code> and it can be set between <code>0</code> and <code>1</code>. (Though the <code>AudioParam</code> returned is read-only, the value it represents is not.)</dd>
 <dt>
  {{domxref("DynamicsCompressorNode.release")}}</dt>
 <dd>
  Is a {{k-rate}} {{domxref("AudioParam")}} representing the amount of time, in seconds, required to increase the gain by 10 dB. It defines how quick the signal is adapted when its volume is reduced. Its default value is <code>0.25</code> and it can be set between <code>0</code> and <code>1</code>. (Though the <code>AudioParam</code> returned is read-only, the value it represents is not.)</dd>
</dl>
<h2 id="Methods">Methods</h2>
<p><em>No specific methods; inherits methods from its parent, </em><em>{{domxref("AudioNode")}}</em>.</p>
<h2 id="Example">Example</h2>
<p>{{page("/en-US/docs/Web/API/AudioContext.createDynamicsCompressor","Example")}}</p>
<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', '#DynamicsCompressorNode-section', 'DynamicsCompressorNode')}}</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>