Companding in communication systems: Which statement about a compandor is FALSE?

Introduction / Context:
Companding (compressing + expanding) is used in analog and digital telephony/audio to improve the perceived signal-to-noise and reduce quantization noise on low-level signals by reshaping dynamic range before and after transmission.

Given Data / Assumptions:

• Compandor performs pre-emphasis (compression) at the transmitter and de-emphasis (expansion) at the receiver.
• Goal: improve SNR for weak portions of the signal.
• Quantization noise is most objectionable for low-level signals in uniform quantization.

Concept / Approach:

Companding law (e.g., μ-law, A-law) increases effective resolution for small amplitudes by mapping them to a larger code range, thus reducing the quantization step relative to the weak signal amplitude and improving the signal-to-quantizing-noise ratio (SQNR) for soft passages.

Step-by-Step Solution:

Verification / Alternative check:

Telephony standards (μ-law/A-law) show improved effective bits for small amplitudes compared to uniform PCM, confirming better SQNR for weak signals.

Why Other Options Are Wrong:

• (a), (b), (d) correctly describe compression, preferential treatment for weak parts, and increased quantum steps traversed for low-level signals after companding.
• (c) is false because companding specifically improves—not worsens—the SQNR of weak portions.

Common Pitfalls:

• Assuming companding benefits only strong signals; the key benefit is for low-level content.

Final Answer:

For weaker signals it gives a poor ratio of signal strength to quantizing error.