If a signal is sampled below the Nyquist rate, which phenomenon occurs?

If a signal is sampled below the Nyquist rate, which phenomenon occurs?

• A. Aliasing is avoided
• B. Quantization error increases
• C. Attenuation of high frequencies
• D. Aliasing occurs due to spectrum replication

Answer: (D)

Sampling below the Nyquist rate causes aliasing. When you sample, the continuous-spectrum repeats every f_s (the sampling frequency). If f_s is less than twice the highest frequency in the signal, these replicated spectra overlap in the baseband. That overlap folds high-frequency content into lower frequencies, so the sampled signal’s spectrum no longer matches the original—this is aliasing due to spectrum replication. Quantization error is a separate issue tied to the ADC’s bit depth, and attenuation of high frequencies is typically due to filtering or channel effects, not the act of undersampling itself.

Sampling below the Nyquist rate causes aliasing. When you sample, the continuous-spectrum repeats every f_s (the sampling frequency). If f_s is less than twice the highest frequency in the signal, these replicated spectra overlap in the baseband. That overlap folds high-frequency content into lower frequencies, so the sampled signal’s spectrum no longer matches the original—this is aliasing due to spectrum replication. Quantization error is a separate issue tied to the ADC’s bit depth, and attenuation of high frequencies is typically due to filtering or channel effects, not the act of undersampling itself.