Which statement correctly describes aliasing risk with sampling rate?

Which statement correctly describes aliasing risk with sampling rate?

• A. Aliasing occurs if Fs > 2*Fmax.
• B. Aliasing occurs if Fs < 2*Fmax.
• C. Aliasing occurs if Fs = 2*Fmax.
• D. Aliasing occurs regardless of Fs.

Answer: (B)

The key idea is the Nyquist criterion: to capture all frequency content without distortion, you must sample at least twice the highest frequency present in the signal. If the sampling rate is lower than twice that maximum frequency (Fs < 2Fmax), the spectral copies created by sampling overlap, causing high-frequency components to appear as lower frequencies—aliasing. That’s why aliasing risk exists when Fs is less than 2Fmax. If Fs is greater than 2Fmax, aliasing can be avoided in an ideal scenario; at Fs = 2Fmax you’re at the limit, where practical non-ideal filters can still allow some aliasing.