Duophonic Keyboard

[Mike I]

Hi guys,
This Oberheim TVS-1 duophonic controller with independent voicing seems 
really neat. I wonder how it works? A trigger/gate for the upper voice 
could be generated whenever the top of string voltage drops (signalling 
that a 2nd key has been pressed). Maybe some sort of simple "state 
machine" that keeps track of gates, triggers, and changes in CV's could 
be dreamed up which would enable independent voicing. Mike I.