PC-2 is a psychoacoustic compressor.
PC-2 features a psycho-acoustic relevance mode. Instead of using a peak or rms-level estimation, this mode employes a perceptual loudness model to compute the loudness of the input signal. This perceptual loudness model is combined with advanced attack and release stages that model peripheral adaptation of the human auditory nerve. The result is a very transparent compression characteristic, even with very short attack and release times.
On the other hand, the simple, classic compression behavior can be engaged too by simply switching off the complex loudness model.