Editing Nyquist rate (section)

{{Short description|Minimum sampling rate to avoid aliasing}}
{{distinguish|Nyquist frequency}}
{{Use American English|date = March 2019}}
[[File:Nyquist frequency & rate.svg|thumb|Fig 1: Typical example of Nyquist frequency and rate. They are rarely equal, because that would require over-sampling by a factor of 2 (i.e. 4 times the bandwidth).]] 

In [[signal processing]], the '''Nyquist rate''', named after [[Harry Nyquist]], is a value  equal to twice the highest frequency ([[Bandwidth (signal processing)|bandwidth]]) of a given function or signal. It has units of [[Sampling (signal processing)|samples]] per unit time, conventionally expressed as samples per second, or [[hertz]] (Hz).<ref name=Oppenheim/> When the signal is sampled at a higher [[Sampling (signal processing)|sample rate]] {{xref|(see {{Slink|Nyquist–Shannon_sampling_theorem|Critical_frequency|nopage=y}})}}, the resulting [[discrete-time]] sequence is said to be free of the distortion known as [[aliasing]].  Conversely, for a given sample rate the corresponding [[Nyquist frequency]] is one-half the sample rate.  Note that the ''Nyquist rate'' is a property of a [[continuous-time signal]], whereas ''Nyquist frequency'' is a property of a discrete-time system.

The term ''Nyquist rate'' is also used in a different context with units of symbols per second, which is actually the field in which Harry Nyquist was working.  In that context it is an upper bound for the [[symbol rate]] across a bandwidth-limited [[baseband]] channel such as a [[electrical telegraph|telegraph line]]<ref name=Freeman/> or [[passband]] channel such as a limited radio frequency band or a [[frequency division multiplex]] channel.