These are vintage FET-compressors originally taken from Helios consoles. The Compex is divided in three sections, which are seperately controllable: a compressor, a peak limiter, and either a gate or an expander. They have a very unique sound compared to other FET-based compressors. The most classic example of the Compex is on the drum sound of "When the Levee Breaks" by Led Zeppelin.