Pulse Code Modulation (PCM) MCQ

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Pulse Code Modulation (PCM) MCQ

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Multiple-Choice Questions

Q.1. In PCM, the quantization noise depends on

  • sampling rate
  • number of quantization levels
  • signal power
  • none of the above

Answer: number of quantization levels

Q.2. Which of the following modulation is digital in nature

  • PAM
  • PPM
  • DM
  • none of the above

Answer: DM

Q.3. Which of the following modulation is analog in nature

  • PCM
  • DPCM
  • DM
  • none of the above

Answer: none of the above

Q.4. In PCM, if the number of quantization levels is increased from 4 to 64, then the bandwidth requirement will approximately be

  • 3 times
  • 4 times
  • 8 times
  • 16 times

Answer: 3 times

Q.5. Quantization noise occurs in

  • PAM
  • PWM
  • DM
  • none of the above

Answer: DM

Q.6. Companding is used in PCM to

  • reduce bandwidth
  • reduce power
  • increase S/N ratio
  • get almost uniform S/N ratio

Answer: get almost uniform S/N ratio

Q.7. Pulse stuffing is used in

  • synchronous TDM
  • asynchronous TDM
  • any TDM
  • none of the above

Answer: asynchronous TDM

Q.8. The main advantage of PCM is

  • less bandwidth
  • less power
  • better performance in presence of noise
  • possibility of multiplexing

Answer: better performance in presence of noise

Q.9. The main disadvantage of PCM is

  • large bandwidth
  • large power
  • complex circuitry
  • quantization noise

Answer: large bandwidth

Q.10. The main advantage of DM over PCM is

  • less bandwidth
  • less power
  • better S/N ratio
  • simple circuitry

Answer: simple circuitry

Q.11. In a DM system, the granular noise occurs when modulating signal

  • increases rapidly
  • decreases rapidly
  • changes within the step size
  • has high frequency component

Answer: changes within the step size

Q.12. Pick the odd man out

  • URZ
  • BRZ
  • Manchester code
  • differential code

Answer: Manchester code

Q.13. The number of bits per sample in a PCM system is increased from 8 to 16. The bandwidth of the system will increase

  • 8 times
  • 2 times
  • 1/2 times
  • 28 times

Answer: 2 times

Q.14. The standard data rate of a PCM voice channel is

  • 8 kbps
  • 8 bps
  • 16 bps
  • 64 kbps

Answer: 64 kbps

Q.15. The signal-to-quantization noise ratio for a sinusoidal signal quantized using 10 bit PCM is:

  • 62 dB
  • 10 dB
  • 60 dB
  • 32 dB

Answer: 62 dB

Q.16. The output SNR in a DM system for a 1 kHz sinusoid sampled at 32 kHz without slope overload and followed by a 4 kHz post-reconstruction filter is given as

  • 30.6 dB
  • 8 dB
  • 24.9 dB
  • 20 dB

Answer: 24.9 dB

Q.17. The line code that has zero d.c. component for pulse transmission of random binary data is

  • UP-NRZ
  • UP-RZ
  • BPRZ-AMI
  • BPNRZ

Answer: BPRZ-AMI

Q.18. The number of bits per sample in a PCM system with sinusoidal input is increased from n to n +1. The improvement in signal to quantization noise ratio will be

  • 3 dB
  • 6 dB
  • 2n dB
  • n dB

Answer: 6 dB

Q.19. The word length of a 64 quantization level PCM for S = 2 is

  • 3
  • 4
  • 5
  • 6

Answer: 6

Q.20. The word length of a 64 quantization level PCM for S = 4 is

  • 3
  • 4
  • 5
  • 6

Answer: 3

Q.21. In a PCM system, the number of quantization levels is 32 and the maximum signal frequency is 4 kHz. The bit transmission rate is

  • 8 kbps
  • 16 kbps
  • 32 kbps
  • 40 kbps

Answer: 40 kbps

Q.22. For a PCM system with 256 quantization levels, the sampling frequency is 10 kHz. The BW is

  • 20 kHz
  • 40 kHz
  • 80 kHz
  • 10 kHz

Answer: 40 kHz

Q.23. The bandwidth required for transmission of high quality speech is

  • 10 kHz
  • 15 kHz
  • 4 kHz

Answer: 15 kHz

Q.24. Consider the following statements comparing delta modulation with PCM systems: DM requires

  1. a lower sampling rate
  2. a higher sampling rate
  3. a large bandwidth
  4. simpler hardware

Which of these statements are correct?

  • 1, 2 and 4
  • 1, 2 and 3
  • 1, 3 and 4
  • 2, 3 and 4

Answer: 2, 3 and 4

Q.25. The ramp signal m(t) = at is applied to a delta modulator with sampling period Ts, and step size δ. Slope overload distortion would occur if

  • δ< a
  • δ> a
  • δ < aTs
  • δ> aTs 

Answer: δ < aTs

Q.26. In asynchronous TDM, for n signal sources, each frame contains m slots, where m is usually

  • less than n
  • 2n
  • n
  • greater than 2n

Answer: n

Q.27. A sinusoidal signal with peak-to-peak amplitude of 1.536 V is quantized in 128 levels using a mid-rise uniform quantizer. The quantization noise power is

  • 0.768 V
  • 48 x 10-6 V2
  • 12 x 10-6 V2
  • 3.072 V

Answer: 12 x 10-6 V2

Q.28. In a PCM system, if the code-word length is increased from 6 to 8 bits, the signal-to-quantization noise ratio improves by the factor

  • 8/6
  • 12
  • 16
  • 8  

Answer: 16

Q.29. In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval t1 < t < t2. This indicates that during this internal

  • the input to the modulator is essentially constant
  • the modulator is going through slope overload
  • the accumulator is in saturation
  • the speech signal is being sampled at the Nyquist rate

Answer: the input to the modulator is essentially constant

Q.30. The minimum step-size required for a delta-modulator operating at 32 K samples/second to track the signal [u(t) being the unit step function]

x(t)=125t[u_{t}-u_{t-1}]+(250-125t)[u_{t-1}-u_{t-2}]

so that slope-overload is avoided, would be

  • 2^{-10}
  • 2^{-8}
  • 2^{-6}
  • 2^{-4}

 Answer: 2^{-8}

Q.31. In delta modulation, the slope overload distortion can be reduced by

  • decreasing the step size
  • decreasing the granular noise
  • decreasing the sampling rate
  • increasing the step size

Answer: increasing the step size

Q.32. Which is the most important sub-system for recovering and reconstructing signals in a TDM system?

  • Envelope detector followed by a low pass filter
  • Synchronization circuit for proper timing
  • Bandpass filters to segregate channels
  • Coherent detector to ensure frequency and phase correction

Answer: Coherent detector to ensure frequency and phase correction

Q.33. Which one of the following is correct?

In a TDM system, each signal is allotted in a frame a unique and fixed

  • frequency slot
  • time slot
  • amplitude slot
  • phase slot

Answer: time slot

Q.34. A speech signal band limited to 4 kHz and peak-to-peak voltage varying between +5 V and -5 V, is sampled at the Nyquist rate. Each sample is quantized and represented by 8 bits. The number of quantization levels required to reduce the quantization noise by a factor of 4 would be

  • 1024
  • 512
  • 256
  • 64

Answer: 512

MCQ on Pulse Code Modulation (PCM)

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