A new direct design technique for ALP recursive digital filters

New methods have been recently reported for the design of approximately linear phase recursive filters using optimization. The structure chosen is a parallel connection of allpass subfilters. A technique is presented which exploits the fact that the transfer function depends only on the phase of each subfilter. By deriving a closed form expression for the phase, it is possible to formulate a set of linear simultaneous equations for each subfilter. The solution of this set gives the coefficients of the transfer function of the subfilter. A design example is given