the mh01 Attenuverting Mixer is a 3-in-1 module: it is a mixer for control voltages or audio, a voltage processor, and a voltage source.

it provides four channels, each with inputs normalled to +5V, a knob for attenuation and polarization (attenuvertion), and an output normalled to the sum.the summing stage provided two modes: DC for control voltages (the LEDs indicate the positive and negative excursions), and AC for audio (DC offset removed, LEDs inactive).so the user could i.e mix audio on three channels and still use the left channel for attenuvertion or as +5V voltage source. or use one input for attenuvertion and a 2nd channel for adding offset, still leaving the two left channels for attenuvertion... or whatever.