Amplitude Effect - Compressor
Compressor - Compressor reduces the dynamic range of a signal (peaks)and allows you to increase the overall volume of the entire signal.
Threshold - The level that the compressor starts to act on the signal.
Ratio - The amount that the compressor affects the signal.
Attack - Controls how soon the compressor kicks in
Release - Controls how long the compressor continues affecting the signal after it has dropped back below the threshold setting.
Gain - Allows you to adjust the level (volume) of the signal going out of the compressor.
Hard Knee or Soft Knee - Angle of Compression and its desired affect. More gradual/less.
Amplitude Effect - Limiter
Limiter - Acts as a barrier pulling up amplitude (volume) but not allowing it to pass over a certain frequency. Usually grouped with the compressor to even out any performance that shows signs of a high degree of unwanted dynamic variation.