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GLOSSARY OF TERMS USED IN TIME SERIES ANALYSIS OF CARDIOVASCULAR DATA

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Error occurring when the sampling frequency of analog-to-digital conversion is lower than twice the highest frequency contained in the signal (Nyquist frequency).

To avoid this error, a low-pass filter able to stop all the components of variability with frequency higher than half the sampling frequency  should be used prior to the sampling process.

Aliasing occurs when the sampling frequency is too low with respect to the frequency content in the original time series. A new, but “false”, frequency is obtained by the sampling procedure.

This figure shows what occurs to the spectrum when the sampling frequency is too low. Spectral components above the Nyquist frequency get folded around f_Nyquist