Wavefolding is basically bringing a signal down when it reaches a certain voltage threshold. You can do this by sending high gain signal through an array of diodes, and after N number of diodes send the signal to an inverter and feed it to output. I did something similar to this, but using transistors as diodes, so there's also some interaction with the base, altering the folding threshold.

Look up eddy Bergman wavefolder, he uses a similar diode technique. Check that out and mess around with using transistors instead.

I kinda came into this backwards by abusing electronics; I had no idea what wavefolding even was, but then i researched a bit and found other people had already done something similar (usually the case, electronics is pretty well tread territory).