Efficient Polynomial Implementation of the EMS VCS3 Filter Model

A previously existing nonlinear differential equation system modeling the EMS VCS3 voltage controlled filter is reformulated here in polynomial form, avoiding the expensive computation of transcendent functions imposed by the original model. The new system is discretized by means of an implicit numerical scheme, and solved using Newton Raphson iterations. While maintaining instantaneous controllability, the algorithm is both significantly faster and more accurate than the previous filter-based solution. A real time version of the model has been implemented under the Pure Data audio processing environment and as a VST plugin.