Used 8NU8R Malekko Heavy Industry Eurorack.
Dual Analog Attenuator & Rectifier

The Malekko 8NU8R is a dual 4hp attenuator, and also has the ability to switch on diode rectification waveshaping. Regular attenuation, as well as full and half wave rectification with adjustable attenuation are possible. When no input is present, each half of the 8NU8R produces a steady DC voltage (offset) adjustable by the level control. Rectification can be used to create subtle distortion effects on audio, or to transform bipolar or unipolar modulation sources into new unipolar waveforms.