The Neve 33609 is a diode bridge compressor. A matched bridge of diodes attenuate the signal based on a control voltage. It is a masterpiece of design.
These circuit boards were designed by IGOR of groupdiy. The threshold and makeup gain use 24 step ELMA switches for fine control.
The 33609 also has a limiter, but the signal fed to the limiter is higher, near the output, and acts to prevent signal clipping downstream.