This module uses two gated oscillators that get turned on and off by a VCO input. The thresholds are controllable with external CV and each oscillator has independent frequency controls. This creates wild new harmonics when mixed back in with the original signal

The price is for the PCBonly
http://bartonmusicalcircuits.com/shop/index.php?route=product/product&product_id=150

https://bartonmusicalcircuits.com/synchres/index.html