Explain the sampling theorem and aliasing.

The sampling theorem (Nyquist-Shannon) states: A bandlimited signal with maximum frequency fmax can be perfectly reconstructed from samples taken at rate fs > 2*fmax. The minimum sampling rate (2*fmax) is the Nyquist rate. Aliasing occurs when fs < 2*fmax: high-frequency components fold back into lower frequencies, causing distortion that cannot be removed after sampling. Prevention: Use anti-aliasing filter (lowpass) before sampling to remove frequencies above fs/2. Practical systems use fs significantly above Nyquist for margin.