Aliasing

Aliasing is an effect that causes different signals to become indistinguishable when sampled. It occurs when a signal is sampled at a rate insufficient to capture its highest frequency components, leading to distortion or misrepresentation of the original signal. The term originates from the fact that higher frequencies are incorrectly mapped or aliased to lower frequencies.

In digital signal processing, aliasing happens when the sampling rate is less than twice the highest frequency component of the signal, violating the Nyquist-Shannon sampling theorem. This results in frequencies above the Nyquist frequency being folded back into the lower frequency range. A common example is the appearance of wagon wheels appearing to rotate backwards in films, which is a visual aliasing effect caused by the frame rate sampling.

Aliasing can be prevented through anti-aliasing filters that remove high-frequency components before sampling, or by increasing the sampling rate sufficiently. In computer graphics, anti-aliasing techniques smooth jagged edges to create more visually appealing images. In audio processing, oversampling and filtering are used to minimize aliasing artifacts.

Understanding and managing aliasing is crucial in various fields including digital audio, telecommunications, medical imaging, and computer graphics, where accurate signal representation is essential.