4-pole (24dB/oct) "Sallen-Key" filter
Nonlinear 2nd kind Butterworth filter of 4th order
This is the 4-pole "Sallen-Key" filter demoed during the talk at the ADC'18
Reaktor structure is not 1:1 the structure shown on the slide, it had to be converted to an equivalent structure to work around the limitations of the ZDF toolkit, but the sound should be identical (except for the realtime modulation of the resonance, where some differences might be observed).
Update 1.0.1: set default saturation level to 1