= Anti-aliasing filter
An <anti-aliasing filter> suppresses signal components outside the intended acquisition band before sampling. For voltage recording it is an analogue filter ahead of the <analog-to-digital converter>, with a transition band allowed below half the sampling rate. Once two frequencies have become indistinguishable through <aliasing>, a digital filter generally cannot recover the lost distinction. The <Nyquist–Shannon sampling theorem> concerns an already <bandlimited function>; a physical filter approximates that prerequisite.
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