# Digital Signal Processing Questions and Answers – Specifications and Classification of Analog Filters

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This set of Digital Signal Processing Multiple Choice Questions & Answers (MCQs) focuses on “Specifications and Classification of Analog Filters”.

1. What is the region between origin and the pass band frequency in the magnitude frequency response of a low pass filter?
a) Stop band
b) Pass band
c) Transition band
d) None of the mentioned

Explanation: From the magnitude frequency response of a low pass filter, we can state that the region before pass band frequency is known as ‘pass band’ where the signal is passed without huge losses.

2. What is the region between stop band and the pass band frequencies in the magnitude frequency response of a low pass filter?
a) Stop band
b) Pass band
c) Transition band
d) None of the mentioned

Explanation: From the magnitude frequency response of a low pass filter, we can state that the region between pass band and stop band frequencies is known as ‘transition band’ where no specifications are provided.

3. What is the region after the stop band frequency in the magnitude frequency response of a low pass filter?
a) Stop band
b) Pass band
c) Transition band
d) None of the mentioned

Explanation: From the magnitude frequency response of a low pass filter, we can state that the region after stop band frequency is known as ‘stop band’ where the signal is stopped or restricted.

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4. 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

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.

5. 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

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.

6. What is the value of pass band ripple in dB?
a) -20log(1- δP)
b) -20log(δP)
c) 20log(1- δP)
d) None of the mentioned

Explanation: 1-δP is known as the pass band ripple or the pass band attenuation, and its value in dB is given as -20log(1-δP).

7. What is the value of stop band ripple in dB?
a) -20log(1-δS)
b) -20log(δS)
c) 20log(1-δS)
d) None of the mentioned

Explanation: δS is known as the stop band attenuation, and its value in dB is given as -20log(δS).

8. What is the pass band gain of a low pass filter with 1- δP as the pass band attenuation?
a) -20log(1- δP)
b) -20log(δP)
c) 20log(δP)
d) 20log(1- δP)

Explanation: If 1-δP is the pass band attenuation, then the pass band gain is given by the formula 20log(1-δP).

9. What is the stop band gain of a low pass filter with δS as the pass band attenuation?
a) -20log(1- δS)
b) -20log(δS)
c) 20log(δS)
d) 20log(1- δS)

Explanation: If δS is the stop band attenuation, then the stop band gain is given by the formula 20log(δS).

10. What is the cutoff frequency of a normalized filter?
d) None of the mentioned

Explanation: A filter is said to be normalized if the cutoff frequency of the filter, Ωc is 1 rad/sec.

11. The low pass, high pass, band pass and band stop filters can be designed by applying a specific transformation to a normalized low pass filter.
a) True
b) False

Explanation: It is known that the low pass, high pass, band pass and band stop filters can be designed by applying a specific transformation to a normalized low pass filter. Therefore, a lot of importance is given to the design of normalized low pass analog filter.

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