The
Nyquist frequency, named after electronic engineer
Harry Nyquist, is half of the
sampling rate of a
discrete signal processing system. It is sometimes known as the
folding frequency of a sampling system. An example of folding is depicted in Figure 1, where f
s is the sampling rate and 0.5 f
s is the corresponding Nyquist frequency. The black dot plotted at 0.6 f
s represents the amplitude and frequency of a sinusoidal function whose frequency is 60% of the sample-rate (f
s). The other three dots indicate the frequencies and amplitudes of three other sinusoids that would produce the same set of samples as the actual sinusoid that was sampled. The symmetry about 0.5 f
s is referred to as
folding.