# Nyquist frequency

The **Nyquist frequency** is a term from signal theory . The term was coined by Claude Elwood Shannon and named after Harry Nyquist and is also known as the **Nyquist limit** . It is defined as half the sampling frequency of a time-discrete system:

According to the underlying Nyquist-Shannon sampling theorem , all components in a signal must have frequencies lower than the Nyquist frequency so that the sampled signal can be reconstructed as precisely as required:

Accordingly, the sampling frequency of the point-by-point sampling from the original signal must be more than twice as high as the highest frequency contained in the original signal :

If this criterion is not complied with, non-linear distortion occurs, which is also referred to as an aliasing effect . These cannot be filtered out again. The lower limit for alias-free sampling is also referred to as the **Nyquist rate** .

## See also

## literature

- Karl-Dirk Kammeyer: message transmission . 4th revised and supplemented edition. Vieweg + Teubner, Wiesbaden 2008, ISBN 978-3-8351-0179-1 .
- Claude E. Shannon: Communication in the Presence of Noise . ( stanford.edu [PDF]).