The block diagram of a typical inexpensive phase shifter for guitar players is shown in Fig.18.104.22.168 It consists of a series chain of first-order allpass filters,9.21 each having a single time-varying parameter controlling the pole and zero location over time, plus a feedforward path through gain which is a fixed depth control. Thus, the delay line of the flanger is replaced by a string of allpass filters. (A delay line is of course an allpass filter itself.)
In analog hardware, the first-order allpass transfer function [452, Appendix E, Section 8]9.22is
We now consider the analog and digital cases, respectively.