Dispersive Delay and Comb Filters Using a Modal Structure
Jonathan S. Abel, Elliot Kermit Canfield-Dafilou · IEEE Signal Processing Letters · 2019
High-order dispersive delays are typically implemented as a cascade of second-order allpass sections, making them difficult to modify in real time and prone to numerical issues. Here, such filters are implemented using a modal architecture-a parallel combination of resonant filters tuned to a set of mode frequencies determined by the desired dispersion characteristic. Two configurations are presented, a “dispersive delay filter” in which a single dispersive arrival is produced, and a “dispersive comb filter” in which a series of increasingly dispersive echoes of the input signal are generated. The parallel structure has computational and numerical advantages. Simple, closed-form techniques for designing the needed mode filter frequencies and amplitudes according to the desired dispersion and equalization are presented, and applied to spring reverberator emulation and decorrelation filter design.