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The highest frequency
in equation (6),
,is almost .This frequency is twice as high as the Nyquist frequency .The **Nyquist frequency**
is normally thought of as the ``highest possible'' frequency,
because , for integer *t*,
plots as .The double Nyquist frequency function,
, for integer *t*,
plots as .So this frequency above the highest frequency is really zero frequency!
We need to recall that .Thus, all the frequencies near the upper end of the range (6)
are really small negative frequencies.
Negative frequencies on the interval were moved to interval by the matrix form of Fourier summation.

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Stanford Exploration Project

10/31/1997