What is the difference between a compressor and a limiter?

A limiter is like a compressor on steroids.

When you compress a sound, the loud parts get quieter and the quiet sections may become louder. This is useful if you want to make your CDs as loud as possible.

Two channel compressor/limiter

If you set the compressor or limiter correctly, the overall volume from beginning to end stays at a high level throughout.

A simple compressor plug-in

The student engineer should not attempt to use a multi-function compressor until he or she has mastered one of the basic models.

The controls usually found on a basic unit are: Input, Output, Attack, Release and Ratio. (25 pages on compressors in the course).