A discrete-time all-pass system has two of its poles at 0.25∠0° and 2 ∠30° Which one of the following statements about the system is TRUE?

Q. A discrete-time all-pass system has two of its poles at 0.25∠0° and 2 ∠30° Which one of the following statements about the system is TRUE?

A. It has two more poles at 0.5Ð30and 4Ð0 .

B. It is stable only when the impulse response is two-sided.

C. It has constant phase response over all frequencies.

D. It has constant phase response over the entire z-plane.

Ans: It is stable only when the impulse response is two-sided.