In sampling theory, Nyquist criterion states that to avoid distortion in sampling a signal, the sampling rate must be at least twice the maximum frequency component.

• A. True
• B. False
• C. Only for baseband signals
• D. Only if the signal is noise-free

Answer: (A)

Avoiding aliasing by choosing a sampling rate that can faithfully represent all spectral content. The idea is that sampling creates copies of the signal’s spectrum spaced at the sampling frequency. If the sampling rate is at least twice the highest frequency present, these copies just touch at the edges without overlapping, so the original signal can be reconstructed from the samples. If the rate is lower, the spectral copies overlap and high-frequency components fold into lower frequencies, producing distortion in the recovered signal. The statement uses the maximum frequency component, which is the standard way to express the minimum sampling rate—for baseband signals this reduces to twice the bandwidth. In practice, you often pick a rate a bit higher to accommodate non-ideal filters and a transition band.