Doepfer

The recent poll on the Nord Modular style clocked random generator 
got me thinking about the Nord Modular's ring modulator.  It has an 
additional control that varies the modulation from ring to AM to 
none, which can also be "voltage" controlled.  This is extremely 
useful and I don't know of an analog ring modulator that does this 
out of the box. 

I have been trying to do something similar using existing modules.  
It is my understanding that ring modulation differs from AM in that  
the carrier is inverted when the modulator is negative. Also, in the 
Nord, when the control is zeroed and there is no modulation, it 
simply passes the carrier unaltered. 

So, to model the nord's ring modulator, I have started by adding an 
offset to the modulator so that it is all positive (or, better, 
negative), then attenuating the signal with a VCA (this attenuation 
is the "ring to am to nothing" control) then adding another offset 
to make the modulator AC again when the VCA is full open, and 
sending that signal to the ring modulator's modulator input.

Is this correct?  Does anybody have an easier way of accomplishing 
this same end?  Does anybody know of an analog ring modulator that 
does this without outboard stuff?  Hey, could this be an idea for a 
new module?