Synthesizer Filters
Will C. Pirkle · Focal Press eBooks · 2021
Filters play a critical role in most synthesizer algorithms, from simple damping in the Karplus-Strong algorithms to searing filter sweeps in analog modeling synths. Zavalishin’s VA design technique simulates analog filters by implementing the analog block diagrams, consisting of summers, multipliers, and integrators, with their digital versions. The summers and multipliers translate easily into their corresponding DSP structures, and there are more than two-dozen different digital integrators that may be considered. This idea goes back to El-Masry’s RLC simulation technique and has been re-packaged over the years in different forms, but it is based on the notion of digital integrator replacement. This method did not gain traction early on because it usually results in delay-free loops, also called “zero delay feedback loops” or “zero delay feedback” or ZDF. Zavalishin presents an algebraic solution to the delay-free loop problem. Korg35 second order resonant filters used in the MS-10 and early MS-20 are voltage controlled versions of the Sallen-Key filter topology.