The 321 includes the most useful functions we always need in every patch, to edit and combine dynamically the signals in use.
It is composed of three identical sections, the red, yellow and green, where each of those is capable of scaling any signal, from 0 up to 2 times (+6dB), flip its phase, and apply a DC offset, allowing to shift your audio or CV up or down.
In case no signals are connected to the section input, the offset may act as a CV source too.
The three sections are then summed together into two independent summing stages: the top right jack outputs the sum of all three sections, while the top left outputs the sum of the unconnected sections only (semi-normalled).
The 321 is entirely DC coupled, allowing the process of control voltages as well as audio signals.
In case CVs or audio signals are particularly hot, the two 6dB attenuators, one per each summing section might be helpful to reduce exactly by the 50% the incoming signals.