Nyquist rate

In <a href="/facts/Signal_processing/Npaja6zb">signal processing</a>, the Nyquist rate, named after <a href="/facts/Harry_Nyquist/BIDzoc9I">Harry Nyquist</a>, is a value equal to twice the highest frequency (<a href="/facts/Bandwidth_(signal_processing)/7eMDzfJI">bandwidth</a>) of a given function or signal. It has units of <a href="/facts/Sampling_(signal_processing)/xxck7aLN">samples</a> per unit time, conventionally expressed as samples per second, or <a href="/facts/Hertz/6Wshj5qm">hertz</a> (Hz). When the signal is sampled at a higher <a href="/facts/Sampling_(signal_processing)/xxck7aLN">sample rate</a> (see <a href="/facts/Nyquist%E2%80%93Shannon_sampling_theorem/JYlVrvc5">§ Critical frequency</a>), the resulting <a href="/facts/Discrete-time/RR8wpS9e">discrete-time</a> sequence is said to be free of the distortion known as <a href="/facts/Aliasing/Pzg84HL0">aliasing</a>. Conversely, for a given sample rate the corresponding <a href="/facts/Nyquist_frequency/zwFUKdVR">Nyquist frequency</a> is one-half the sample rate. Note that the Nyquist rate is a property of a <a href="/facts/Continuous-time_signal/RR8wpS9e">continuous-time signal</a>, 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 <a href="/facts/Symbol_rate/YlQ3JHVr">symbol rate</a> across a bandwidth-limited <a href="/facts/Baseband/yC0jJwbL">baseband</a> channel such as a <a href="/facts/Electrical_telegraph/yrFhbvM8">telegraph line</a> or <a href="/facts/Passband/VebMrazm">passband</a> channel such as a limited radio frequency band or a <a href="/facts/Frequency_division_multiplex/lgj6TMU1">frequency division multiplex</a> channel.

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Nyquist rate