DynamicsCompressorNode.knee

The knee property of the DynamicsCompressorNode interface is a k-rate AudioParam containing a decibel value representing the range above the threshold where the curve smoothly transitions to the compressed portion.

The knee property's default value is 30 and it can be set between 0 and 40.

Describes the effect of a knee, showing two curves one for a hard knee, the other for a soft knee.

Syntax

var audioCtx = new AudioContext();
var compressor = audioCtx.createDynamicsCompressor();
compressor.knee.value = 40;

Value

An AudioParam.

Note: Though the AudioParam returned is read-only, the value it represents is not.

Example

The below code demonstrates a simple usage of createDynamicsCompressor() to add compression to an audio track. For a more complete example, have a look at our basic Compressor example (view the source code).

// Create a MediaElementAudioSourceNode
// Feed the HTMLMediaElement into it
var source = audioCtx.createMediaElementSource(myAudio);

// Create a compressor node
var compressor = audioCtx.createDynamicsCompressor();
compressor.threshold.setValueAtTime(-50, audioCtx.currentTime);
compressor.knee.setValueAtTime(40, audioCtx.currentTime);
compressor.ratio.setValueAtTime(12, audioCtx.currentTime);
compressor.attack.setValueAtTime(0, audioCtx.currentTime);
compressor.release.setValueAtTime(0.25, audioCtx.currentTime);

// connect the AudioBufferSourceNode to the destination
source.connect(audioCtx.destination);

button.onclick = function() {
  var active = button.getAttribute('data-active');
  if(active == 'false') {
    button.setAttribute('data-active', 'true');
    button.innerHTML = 'Remove compression';

    source.disconnect(audioCtx.destination);
    source.connect(compressor);
    compressor.connect(audioCtx.destination);
  } else if(active == 'true') {
    button.setAttribute('data-active', 'false');
    button.innerHTML = 'Add compression';

    source.disconnect(compressor);
    compressor.disconnect(audioCtx.destination);
    source.connect(audioCtx.destination);
  }
}

Specifications

Specification Status Comment
Web Audio API
The definition of 'knee' in that specification.
Working Draft  

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome Full support 14Edge Full support 12Firefox Full support 25IE No support NoOpera Full support 15Safari Full support 6WebView Android Full support YesChrome Android Full support 18Edge Mobile Full support YesFirefox Android Full support 26Opera Android Full support 15Safari iOS ? Samsung Internet Android Full support Yes

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown

See also

Document Tags and Contributors

Contributors to this page: Sheppy, SphinxKnight, fscholz, erikadoyle, chrisdavidmills
Last updated by: Sheppy,