ABSTRACT
Dynamics processors are designed to automatically control the amplitude, or gain, of an audio signal and consist of two families: compressors and expanders. Technically speaking, compressors and expanders both change the gain of a signal after its level rises above a predetermined threshold value. A compressor reduces the gain of the signal once it goes over the threshold. An expander raises the gain of a signal after it crosses above the threshold. With the exception of noise reduction systems, true expanders are rare since they can easily cause instabilities, runaway gain, and distortion. What is normally called an “expander” today is technically a downward expander . A downward expander reduces the gain of a signal after it drops below the threshold. We will be designing a downward expander but will use the common lingo and refer to it simply as an expander. Both compressors and expanders require the user to decide on the threshold of operation as well as a ratio value that tells the device how much gain reduction to implement.
