The first step in becoming familiar with digital filters is to learn to speak the language used in the filter business. Fortunately, the vocabulary of digital filters corresponds very well to the mother tongue used for continuous (analog) filters—so we don't have to unlearn anything that we already know. This appendix is an introduction to the terminology of digital filters.
Allpass filter—. an IIR filter whose magnitude response is unity over its entire frequency range, but whose phase response is variable. Allpass filters are typically appended in a cascade arrangement following a standard IIR filter, H1(z), as shown in Figure F-1.
Figure F-1. Typical use of an allpass filter.
An allpass filter, Hap(z), can ...