Digital Signal Processing Laboratory Viva Questions - Part 9

Q.1- How many real and complex multipliers are required to implement 8 point radix-2 FFT algorithm.

1. 12 & 48
2. 48 &12
3. 64 &56
4. 12 &64
   
   
   
   

Q.2- What is the first stage output of DIT-FFT when input is x(n)={1,1,1,1,0,0,0,0}

1. {1,1,1,1,0,0,0,0}
   
   
2. {1,0,1,0,1,0,1,0}
   
   
3. {1,1,1,1,1,1,1,1}
   
   
4. {1,0,1,0,0,0,0,0}
   
   
5. None of the above

Q.3- What is the first stage output of DIF-FFT when input is x(n)={1,1,1,1,0,0,0,0}

1. {1,1,1,1,0,0,0,0}
   
   
2. {1,1,1,1,1,1,1,1 }
   
   
3. {1,0,1,0,1,0,1,0}
   
   
4. {1,0,1,0,0,0,0,0}
   
   
5. None of the above
   
   

Q.4- If we cascade two identical Butterworth High pass filters, then

(i) 3-dB cut-off frequency will increase

(ii) Gain in pass band increases

(iii) Gain in stop band increases

Which of the following is correct?

(a) (i) only

(b) (i) and (ii)

(c) (i) and (iii)

(d) (ii) only

Q.5- If we sampled a signal m(t) at sampling rates f_s1 and f_s2 (both are more than Nyquist rate) to get discrete signals m(n/ f_s1 ) and m(n/ f_s2 ) , if f_s2> f_s1, and we have only two analog Butterworth reconstructing filters with different order. Then

(i) We will prefer higher order filter for reconstruction of m(n/ f_s2 ), and lower order filter for m(n/ f_s1 )

(ii) We can reduce the cost of the reconstruction filter with high sampling rate

Which of the following is correct?

1. (i) only
2. (ii) only
3. Both (i) and (ii)
4. None of the above

Q.6- (i) If N (order of the stable filter) is even, then Butterworth filters have real pole at s= w_c

(ii) If N is even then Butterworth filters have real pole at s= -w_c

(iii) For the function, if w_c is fixed, then we can change 3-dB cut-off frequency by changing N.

Which of the following is correct?

1. (i) Only
2. (ii) only
3. Both (i) and (iii)
4. None of the above

Q.7- Let x(n) be a sequence of length 1024 that is to be convolved with a sequence h(n) of length L. For what values of L is it more efficient to perform the convolution directly than it is to perform the convolution by taking the inverse DFT of the product X (k)H(k) and evaluating the DFTs using a radix-2 FFT algorithm?

1. L < 44
2. L < 34
3. L < 33
4. L < 50

Statement for Q.8-9:

If the specifications for an analog low-pass filter are to have a 1-dB cutoff frequency of 1 kHz and a maximum stopband ripple δ_s = 0.01 for If f > 5 kHz.

Q.8- Determine the required filter order for low pass Butterworth filter:

1. 5
2. 6
3. 3
4. 4

Q.9- Determine the required filter order for low pass filter:

1. 5
2. 6
3. 3
4. 4

Q.10- Find the minimum order of a continuous-time Butterworth filter that will satisfy the following Frequency response constraints:

f_p = 6 KHz, f_s = 10 KHz, passband ripple = 0.1 and stopband attenuation = 0.2

1. 4
2. 5
3. 6
4. None of the above

Ans Key:

1. b
2. c
3. b
4. a
5. b
6. d
7. c
8. d
9. c
10. b