Pulse Code Modulation Questions and Answers

Answer: A

The maximum dynamic range is 98.08 dB.

For an n-bit linear quantizer with a full-scale sinusoidal input, the signal to quantization noise ratio, which sets the usable dynamic range, is

\[ \begin{aligned} \text{SQNR} &= 1.76 + 6.02n\ \text{dB} \\ &= 1.76 + 6.02 \times 16 \\ &= 1.76 + 96.32 = 98.08\ \text{dB} \end{aligned} \]

Each extra bit adds about 6 dB. The value 49.04 dB is half the answer, 32 dB is twice the number of bits, and 16 dB is the number of bits itself, none of which is a decibel ratio for 16 bits.

Answer: D

DPCM exploits the correlation between samples to decrease the encoding rate.

Successive samples of signals such as speech and video are strongly correlated, so each sample can be predicted well from earlier ones. DPCM transmits only the difference between the actual sample and its prediction. That difference has a smaller range than the sample itself, so fewer bits are needed and the bit rate falls.

The options with 'increase' get the purpose backwards. 'Autocorrelation' names the same statistical dependence, but the standard description, and the key, speak of the correlation between samples.