Engineering Dictionary of Terms
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Nyquist. A theorem that determines the minimum sampling rate of a signal so that the original frequency is preserved. A Sampling theorem.
Nyquist Interval. The interval in time between minimum sampling times, which is also half the bandwidth of the signal being sampled. The maximum time interval between equally spaced samples of a signal that will enable the signal waveform to be completely determined.
Nyquist Rate. The reciprocal of the Nyquist interval, the minimum theoretical sampling rate that fully describes a given signal, i.e., enables its faithful reconstruction from the samples.
Aliasing, Under-Sampling
Under-Sampling or aliasing is shown in the graphic with the blue signal being the input and the orange sine wave the under-sampled output. The minimum sampling rate was not followed.
Aliasing. The occurrence of spurious signals in an output signal that were not present in the input signal due to under-sampling [fold-over of the higher frequencies]. The error introduced in a system that is not able to sample a signal at the required frequency. A Digitizing circuit that does not operate to the required incoming frequency producing a completely different frequency at the output.
Aliasing Effect. The apparent downward shift in frequency of components which are higher than one-half the sampling frequency resulting from a sampling rate which is too low in frequency.
