Translations:The Nyquist frequency/14/en

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Let us pick a sampling increment of 0.004 s, so that the sampling frequency is 250 Hz (the Nyquist frequency is thus 125 Hz). Figures 6 and 7 illustrate the impossibility of distinguishing sampled signals outside of the Nyquist range — that is, within the range from –125 Hz to 125 Hz. Let the actual frequency be f and the sampling frequency be . In each of these figures, the aliased frequency is given by . If the resulting is negative, replace it by . We can do this because (for real signals) a positive frequency cannot be distinguished from its negative counterpart. For example, in Figure 7a, the actual frequency is 175 Hz. Thus, the aliased frequency is 250 –175 = 75 Hz.