Compressor Limiters

A compressor is a downward-limiting amplifier with a ratio of 1:10 or less.  A limiter is the same thing but with rations of 1:10 and higher.  The way it works is when a signal (say your voice) is loud enough to reach a threshold (that you generally set manually) an amplifier circuit works in reverse, proportionate to how many decibels the signal exceeds the threshold.  Say your compressor is adjusted to a 1:3 ratio. For every three dB your voice exceeds the threshold, only 1 dB will pass.  

Back in the old days engineers used compressor limiters to limit the dynamic range of a sound or entire mix to fit within the limitations imposed by mastering for vinyl records and/or for broadcast on AM and then FM radio as well as television broadcast.

Today most of our clients are using compression as an artistic shading (or bludgeoning!) tool.  Some types of compression circuits include optical compression revered for slower, more gentle envelope control and FET limiting which has historically been used for faster attack & release times, useful for faster-tempo music and entire mixes.