Aliasing - definition of
Aliasing - definition of
Aliasing is a phenomenon that occurs during digital sampling of analogue signals, which consists in an incorrect representation of their actual frequency content. Aliasing occurs, when the sampling frequency is too low in relation to the highest frequency contained in the signal, it occurs when the sampling frequency is too low in relation to the highest frequency contained in the signal, which leads to overlapping of harmonic spectra and creation of distorted, false components in the received digital signal.
The theoretical basis for avoiding aliasing is the Nyquist theorem-Shannon, which assumes, that in order to faithfully reproduce a signal, it should be sampled at a frequency at least twice as high as its highest component. If this condition is not fulfilled, the higher frequencies are "folded" into the lower ones, causing difficult to filter out artefacts in signal analysis.
Aliasing can occur in both the time and space, aliasing can occur in both the spatial and temporal domains - so it applies not only to audio or electrical signals, but also in image processing, in which it manifests itself as line distortions, moiré patterns or misrepresentation of details. A typical method of reducing this effect is to use analogue low-pass filters before the sampling process. Such filters, called anti-aliasing, are designed to eliminate frequencies above half the sampling frequency, thereby reducing the risk of misrepresentation.
In engineering practice, an understanding of aliasing is important in the design of systems data acquisition, digital signal converters and in spectral analysis. Incorrectly selected sampling rates can lead to false conclusions and incorrect signal diagnostics, therefore, anti-aliasing is a key element for correct information processing in digital systems.
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