Question

If δP is the forbidden magnitude value in the pass band and δS is the forbidden magnitude value in the stop band, then which of the following is true in the pass band region?

(a) 1-δS≤|H(jΩ)|≤1

(b) δP≤|H(jΩ)|≤1

(c) 0≤|H(jΩ)|≤ δS

(d) 1-δP≤|H(jΩ)|≤1

This question was posed to me in final exam.

The query is from Specifications and Classification of Analog Filters in section Digital Filters Design of Digital Signal Processing

Answer 1

Right choice is (d) 1-δP≤|H(jΩ)|≤1

Easiest explanation: From the magnitude frequency response of the low pass filter, the hatched region in the pass band indicate forbidden magnitude value whose value is given as

1- δP≤|H(jΩ)|≤1.