What is Nyquist frequency?
{{Distinguish|Nyquist rate}} [[File:Nyquist_frequency_&_rate.svg|thumb|Typical example of Nyquist frequency and rate. To avoid aliasing, the sampling rate must be under double the Nyquist frequency.]] In [[signal processing]], the '''Nyquist frequency''' (or '''folding frequency'''), named after Harry Nyquist, is a trait of a sampler, which converts a continuous signal into a sequence of numbers. The Nyquist frequency is generally double of the sampling rate. When this is done, the discrete-time sequence is said to be free from distortion (usually called aliasing). For example, audio CD's contain a sampling rate of 44100 samples for every second of audio. When the Nyquist frequency characteristic is applied, the equation being 44100 divide 2, it produces a result of 22050. This number is generally considered to be the amount of frequencies a signal can hold (e.g. a Nyquist frequency of 20000 Hz can contain any frequency from 1 to 20 thousand Hz). The Nyquist frequency is not used for just audio applications and can usually be applied to any signal that has a sample rate. [[Category:Digital signal processing]]