Compression, limiting, and expansion attenuate or boost audio differently by amplitude.

Evidence

A dynamic range controller, a.k.a. a compressor, attenuates sound the more the level increases beyond a certain threshold. A limiter is a similar effect, but limits the level of signal to a preset value. An expander, on the other hand, leaves large amplitudes untouched, but increasingly amplifies the signal the smaller the amplitude is. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 1950

Categorization

• DEFINE: Clear three-way distinction between compressor, limiter, and expander behavior.