Designing Software Synthesizer Plugins in C++, 2nd Edition

12     Synthesizer Filters

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. Interestingly, many classical DSP textbooks explain the design theory, but they rarely reveal the implementations that we need in audio applications: independent controls for cutoff frequency (f_c) and quality factor (Q) and stability over the audio spectrum from 20 Hz to ~20,480 Hz (10 octaves). Early digital synth filters, designed directly in the z-plane, can be found in Chamberlain, F.R. Moore, and Dodge and Jerse. In the late 1980s, Motorola introduced a set of DSP application notes that demonstrated algorithms with independent controls and which were ...