In actual practice, wave spectra can be computed by
different methods. The most commonly used algorithm is
the fast-Fourier transform (FFT), developed by Cooley
and Tukey (1965). A much slower method, now superseded
by the FFT, is the auto-correlation approach
according to the Wiener-Kinchine theorem, introduced
for practical use by Blackman and Tukey (1959) (see also
Bendat and Piersol, 1971). Experience has shown that
the difference between spectra computed by any two
methods does not exceed confidence limits of each of
them.