Fabfilter PRO-C is a compressor/limiter plugin. But what does a compressor really do? To understand this we have to go back in time when professional studio's didn't use any compressors. The recording engineers had to manually control the faders in order to compensate for any changes in level. This was even before mix automation. John B. Howell was the first one to come up with the idea to develop a device which could control the level of audio signals. The first (experimental) version didn't have any variable settings and acted more like a limiter. Still recording engineers wanted it because saved them a lot of effort. Since then the compressor has been evolving till current day even in the digital realm.