Compression was introduced in recording to help the recording engineer cope with the problems recording live music. For the VCA in a compressor to react, a certain level has to be reached. This is called the threshold. When the input level of a compressor exceeds the threshold set, the compressor's VCA starts to reduce the input level that has exceeded that threshold. The amount the signal is decreased is determined by the ratio.
Most compressor limiters have at least three basic controls.
They are the threshold adjust, the compression ratio amount, and the output gain. If for instance you would only like to trim off the peaks from your synthesizer that feed into your stage amplifier, you would play your loudest passages and then set the threshold to react to those levels. Next check the softer passages. Be sure the threshold indicators not being triggered. If it is flickering, you're threshold is set too low and you will be compressing the whole program.