Question

A PCM system is to have a signal-to-noise ration of 40 dB. The signals are speech and an rms-to-peak ratio of – 10 dB is allowed for. The number of bits per code word is 
1. 6 bits
2. 7 bits
3. 8 bits
4. 10 bits

Answer 1

Correct Answer - Option 2 : 7 bits

Concept:

The Signal to Noise (SNR) Ratio for a PCM system is given by:

SNR = 1.8 + 6n dB

Where ‘n’ is the number of bits per sample.

Analysis:

SNR = 40 dB

40 = 1.8 + 6n

6n = 38.2 

n = 6.4