What is an Audio Compressor?
Compressors control the overall amplitude of a signal by reducing that part of the signal which exceeds an adjustable level (threshold) set by the user. When the signal exceeds the threshold level, the overall amplitude is reduced by a ratio, also usually adjustable by the user. For example, if the ratio of compression is set for 2:1, any part of the signal exceeding the threshold level is reduced by one-half.
An audio compressor is a sound processing tool designed to reduce the dynamic range of the input audio signal. It functions by “turning down” relatively loud audio signals, and “turning up” softer audio signals. It's main purpose is to smooth the audio signal by eliminating or limiting peaks in the audio response. Because compression onset can be variable, it can also modify the attack and decay characteristics of the audio signal. Compressors are available in a stomp box, in a studio rack format, as well as a software plugin. Compressors increase the apparent sustain of stringed instruments such as guitar and bass by bringing up the level of the instrument as the note decays (gets softer). Unfortunately, this also results in the noise floor being increased as well since a compressor generally does not differentiate between noise and audio signal.