Audio frequency applications of PCAS and related filters

This paper considers the design of various filters composed of allpass subfilters approximating multiband, multi-level responses. These include M-level PCAS filters, tree structures of half-band recursive filters and cosine-modulated allpass-based filter banks. Design methods for designing the allpass subfilters in terms of phase are given. It is also shown how to obtain good linear phase across the entire frequency band by modifying the subfilter phase behaviour of the prototype recursive N^th band filter