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.