DynamicsCompressorNode - Web APIs 编辑

The DynamicsCompressorNode 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. DynamicsCompressorNode is an AudioNode that has exactly one input and one output; it is created using the AudioContext.createDynamicsCompressor() method.

Constructor

DynamicsCompressorNode()

Creates a new instance of an DynamicsCompressorNode object.

Properties

Inherits properties from its parent, AudioNode.

DynamicsCompressorNode.threshold Read only

Is a k-rate AudioParam representing the decibel value above which the compression will start taking effect.

DynamicsCompressorNode.knee Read only

Is a k-rate AudioParam containing a decibel value representing the range above the threshold where the curve smoothly transitions to the compressed portion.

DynamicsCompressorNode.ratio Read only

Is a k-rate AudioParam representing the amount of change, in dB, needed in the input for a 1 dB change in the output.

DynamicsCompressorNode.reduction Read only

Is a float representing the amount of gain reduction currently applied by the compressor to the signal.

DynamicsCompressorNode.attack Read only

Is a k-rate AudioParam representing the amount of time, in seconds, required to reduce the gain by 10 dB.

DynamicsCompressorNode.release Read only

Is a k-rate AudioParam representing the amount of time, in seconds, required to increase the gain by 10 dB.

Methods

No specific methods; inherits methods from its parent, AudioNode.

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.textContent = 'Remove compression';

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

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

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Using the Web Audio API