# 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:

${\ displaystyle f _ {\ text {nyquist}} = {\ frac {1} {2}} \ cdot f _ {\ text {scan}}}$

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:

${\ displaystyle f _ {\ text {signal}}

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 : ${\ displaystyle f _ {\ text {signal}}}$

${\ displaystyle f _ {\ text {scan}}> 2 \ cdot f _ {\ text {signal}}}$

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 .