The CompressorNode collects audio data from all of its inputs and applies a compressor filter before passing the data along to its outputs.
Common Uses
- Preventing a sound (or group of sounds) from becoming too loud
Using the CompressorNode
Compressor filters reduce the volume of sounds that go above a certain threshold, according to a specified ratio. The volume is calculated according to this formula:
(NOTE) VolumeAdjustmentDecibels = (1.0 - (1.0 / Ratio)) * (ThresholdDecibels - CurrentVolume)
In other words, if the Ratio is 4.0, the ThresholdDecibels is -2 dB, and the current volume of the sound is +2 db, a volume adjustment of -3 dB will be applied and the volume of the sound will be reduced to -1 dB. If the Ratio property is set to 0.0, the 1.0 - (1.0 / Ratio) value will be set to 1.0, so the volume will never go above the ThresholdDecibels value: this creates a Limiter filter.
The AttackMillisec and ReleaseMillisec properties control how quickly the filter eases in and out as the sound goes above the ThresholdDecibels then goes back below. The AttackMillisec should generally be short and the ReleaseMillisec should be longer, but this will depend on the desired effect. The KneeWidth property sets the number of decibels, centered at the ThresholdDecibels, over which the volume compression eases in.