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Collaboration, Voice & AV · Intermediate

Aliasing

Distortion created when frequencies above half the sampling rate are sampled and appear as false lower frequencies.

Definition

Analog-to-digital converters use anti-aliasing low-pass filters to remove content above the Nyquist frequency before sampling. In video, aliasing appears as jagged edges or moire patterns from insufficient spatial sampling. Oversampling and good filtering reduce aliasing artifacts.

Example

A 30 kHz tone sampled at 48 kHz without filtering appears as an 18 kHz alias.

Exam tip

Aliasing is prevented before sampling with a low-pass filter; it cannot be removed afterward.

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