Allpass filter design using projection-based method under group delay constraints

A new technique for designing digital all-pass IIR filters is proposed. The approach is based on the vector space projection method. Constraint sets, and their associated projectors, that capture the properties of the desired group delay are given. Examples that demonstrate the advantages and flexibility of this method as well as comparisons with a well-known method (Nguyen et al., 1994) are furnished.