Aliasing occurs when sampling below the Nyquist rate. What is the consequence?

• A. The signal is perfectly reconstructed.
• B. New frequencies appear above the Nyquist rate.
• C. High-frequency content folds into lower frequencies, causing distortion.
• D. The sampling rate automatically increases.

Answer: (C)

Aliasing happens because the spectrum of a sampled signal repeats at multiples of the sampling frequency, and if the sampling rate is below twice the highest frequency present, these spectral copies overlap. When that overlap occurs, energy from high-frequency parts folds into lower frequencies in the sampled data, so high-frequency content appears as lower-frequency components. This makes the reconstructed signal distort because it no longer accurately represents the original waveform. For example, sampling a 3 kHz tone at 4 kHz can make it look like a 1 kHz tone after sampling. So the consequence is distortion due to aliasing, not perfect reconstruction, not new frequencies above Nyquist, and not an automatic increase in sampling rate.