From NonLinear Circuits website:
This module started out as an attempt to develop yet another chaos circuit by linking different nonlinear sub-circuits in series, from Chaotic Oscillator Based on Delay Line - Milan Stork. Then I noticed it was folding the waves at different offsets and kind of got diverted into developing a wavefolder.
It is similar in concept to other diode based wavefolders out there, but as this one uses two different nonlinear stages (twice each) rather than the same circuit 4 or 6 or 8 times, the folding is more complex, unbalanced and well, not very neat. What does this mean? It can be noisy.
There was a spare half of the LM13700 sitting there, so I added a VCA with fuzz, similar to the bottom circuit in the NLC VCAs module. The 3rd stage output of the wavefolder goes to the switching pin of the VCA input and the main input of the wavefolder goes to the switching pin of the VCA CV input. Using the offset pot gets it into ringmodulator territory, although this will also affect how the input signal will travel thru the wavefolding stages. This gives a 3rd output from the wavefolder (along with the main out and pulse out), which is even harsher than the main out. Otherwise, you can simply use it as a regular VCA or voltage controlled fuzz/distortion.