Anti-Aliasing Filter
A low-pass filter applied before sampling to attenuate frequency components that would otherwise alias into the representable spectrum.
Sampling Context
An anti-aliasing filter attenuates frequency components above the bandwidth that can be represented safely before analog-to-digital conversion. Practical filters require a transition band, so acquisition systems normally leave a guard band below the theoretical Nyquist limit.
Measurement Boundary
An anti-aliasing filter cannot repair aliasing that has already occurred after sampling. Its relevant specifications include passband ripple, stopband attenuation, transition width, and phase behavior.