Design and implementation of cascaded allpass digital filter structures with magnitude and delay constraints

Considers a filter structure made up from a parallel arrangement of two allpass subfilters. Such structures were used originally in multi-rate problems but have also been applied to conventional filtering. The authors examine the design process and look at approaches using single-line and dual-line templates, the latter being used in conjunction with simulated annealing which gives a finite wordlength solution directly. Furthermore, they describe how this structure can be modified to cope with bandpass and multiple bandpass requirements. Hardware implementation is briefly discussed too and the paper concludes with some design examples illustrating the two methods