Attack: Adjusts how quickly the compressor starts to work after the signal exceeds the compression threshold.
Release: Controls how soon the compressor will stop after the signal goes below the compression threshold.
Ratio: Controls how much compression is applied. For example, a 3:1 ratio means that every time the input signal crosses the threshold by 3dB, output signal will be attenuated 1dB.
Threshold: The Threshold is the level above which the compressor considers the signal too loud and starts applying compression.
Knee: Knee and Attack have a lot in common, but they are not the same. Like Attack, Knee controls how the compressor will react once input signal passes the threshold. Hard Attack makes the compressor engage immediately while Soft Knee shapes its attack time to make it slower and smoother.