Q8Digital Signal Processing
Question
Q.8. What is meant by aliasing? How to avoid it?
Answer
Aliasing is the distortion where higher frequencies masquerade as lower frequencies when a signal is sampled below the Nyquist rate; it is avoided by sampling at fs ≥ 2B or by using an anti-aliasing low-pass filter before sampling.
Aliasing occurs when a signal is sampled at a rate lower than the Nyquist rate (fs < 2B), causing the spectral replicas created by sampling to overlap, so that high-frequency components become indistinguishable from (appear identical to, i.e., are 'aliased' as) lower-frequency components in the sampled signal, resulting in irrecoverable distortion. Aliasing is avoided by ensuring the sampling frequency satisfies fs ≥ 2B (the Nyquist criterion), and in practice by first passing the analog signal through an anti-aliasing low-pass filter that removes/attenuates any frequency content above fs/2 before the signal is sampled, guaranteeing the band-limiting assumption of the sampling theorem is satisfied.