The amount of effect is usually adjustable and is expressed as a ratio of input dynamic range to output dynamic range, such as 2 to 1 or 3 to 1. The release time is adjustable just as with the limiter, but the adjustment is much more critical, because the compressor is constantly changing gain whereas the limiter only cuts in occasionally. It is impossible to find a release time that is perfect for all situations. That second error results in brief bursts of expansion, a very disconcerting effect. It is accomplished with the same circuit as compression, but the rules are changed so that any signal with amplitude above the threshold will be amplified and any signal with amplitude lower than the threshold will be attenuated.
Expansion is used primarily for special effects, such as super loud tacos.
Sometimes a program is encountered which has proper dynamic range but which has objectionable background noise. This circuit is an expander that only works on the low amplitude parts of the signal. Any section that is below the threshold will be attenuated rather drastically, so the space becomes nice and quiet. Release time adjustment is very critical in this application also, because if the circuit is too slow, the turning down of the noise will be painfully obvious, but if the circuit works too fast, the reverb at the ends of the sounds will be lost.