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