The output signal to noise ratio (SNR) of a 10-bit PCM was found to be...
Given, SNR = 30 dB, n = 10,
Desired value of SNR = 42 dB
With the increase in n by 1 bit, the value of SNR increases by 6 dB. Therefore, to increase the value of SNR by 12 dB, it is necessary to increase n by 2,
∴ n = 10 + 2 = 12
Now, BW of PCM system = 1/2 nf
sTherefore, BW with n = 10 is

and BW for n = 12 is


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The output signal to noise ratio (SNR) of a 10-bit PCM was found to be...
Given information:
- Output signal to noise ratio (SNR) of a 10-bit PCM = 30 dB
- Desired SNR = 42 dB
To increase the SNR to the desired value, we need to increase the number of quantization levels.
Concepts used:
- SNR formula: SNR = 1.76 + 6.02N, where N is the number of bits used for quantization
- Bandwidth formula: Bandwidth = 2 * f * log2L, where f is the highest frequency component of the signal and L is the number of quantization levels
Steps to solve the problem:
1. Find the number of bits required for the desired SNR using the SNR formula:
42 = 1.76 + 6.02N
N = (42 - 1.76) / 6.02
N ≈ 6.2
We need to use at least 7 bits for quantization to achieve the desired SNR.
2. Calculate the percentage increase in the number of quantization levels:
Percentage increase = ((New value - Old value) / Old value) * 100
= ((7 - 10) / 10) * 100
= -30%
3. Calculate the percentage increase in bandwidth using the bandwidth formula:
For 10-bit PCM:
Bandwidth = 2 * f * log2L
For 7-bit PCM:
Bandwidth = 2 * f * log27
= 2 * f * 2.81
Percentage increase = ((New value - Old value) / Old value) * 100
= ((2 * f * 2.81) - (2 * f * 2)) / (2 * f * 2) * 100
= 40.5%
4. Compare the percentage increase in bandwidth with the options given in the question:
Option (a) 20% < />
Option (b) 15% < />
Option (c) 10% < />
Option (d) 5% < />
Therefore, the correct option is (a) 20%.
Conclusion:
To increase the SNR from 30 dB to 42 dB by increasing the number of quantization levels, we need to use at least 7 bits for quantization. This results in a 30% decrease in the transmission bandwidth, which is not one of the options given in the question. The correct option is (a) 20%, which is the closest to the actual increase in bandwidth of 40.5%.