The block diagram of a typical inexpensive phase shifter for guitar players is shown in Fig. 3.10. It consists of a series chain of first-order allpass filters,4.4 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.
In analog hardware, the first-order allpass transfer function [426, Appendix C, Section 8]4.5is