where ( \omega ) is normalized frequency (0 to ( \pi )).
1. Introduction In signal processing, most filters are designed to modify the magnitude of a signal’s frequency components — boosting bass, cutting treble, or removing noise. But there exists a special class of filters that leaves the magnitude spectrum completely untouched while selectively shifting the phase of different frequencies. These are called all-pass filters . allpassphase
For a second-order all-pass filter: