antialiasingfilters

An anti-aliasing filter is a signal processing component used to limit the bandwidth of a signal before it is sampled, in order to prevent aliasing when converting from continuous to discrete time. By attenuating frequency components above a certain cutoff, it reduces the risk that high-frequency content folds into the baseband and corrupts the digital representation.

According to the sampling theorem, a signal must be sampled at least twice its highest frequency. Therefore, the filter’s cutoff is typically placed near the Nyquist frequency (half the sampling rate). A brick-wall ideal filter would perfectly suppress all frequencies above this limit, but real filters are imperfect, with a transition band, ripple, and finite stopband attenuation.

Implementation can be analog, placed before an analog-to-digital converter, or digital, applied after sampling as part of a resampling or reconstruction stage. Common designs use low-pass filters, either finite impulse response (FIR) with linear phase, or infinite impulse response (IIR) filters. FIR filters preserve waveform shape at the cost of more coefficients; IIR filters can achieve sharper attenuation with fewer taps but may distort phase. In many systems, the anti-aliasing requirement is met with multi-stage filtering, combining a rough pre-filter with a sharper digital stage.

Applications span audio, video, image sensors, and data resampling. In audio, they reduce pre-ADC high-frequency noise. In imaging and cameras, anti-aliasing filters help prevent moiré and false detail when sensor images are downsampled or processed. The design balances passband fidelity, transition width, stopband attenuation, and computational cost.