The block diagram of a typical inexpensive phase shifter for
guitar players is shown in Fig.8.23.9.20 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.