Question

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

(a) 1- δP≤|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 an interview.

My question is based upon Specifications and Classification of Analog Filters topic in portion Digital Filters Design of Digital Signal Processing

Answer 1

Right answer is (c) 0≤|H(jΩ)|≤ δS

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

0≤|H(jΩ)|≤ δS.