Before revision: Blackman–Tukey transformation method The method is fully described in Blackman and Tukey's book "The measurement of power spectra, from the point of view of communications engineering" and is outlined by the following procedures: Calculate the autocorrelation function with the data Apply a suitable window function, and finally Compute a discrete Fourier transform (now done with FFT) of the data to obtain the power density spectrum Autocorrelation makes the wave smoothed rather than averaging several waveforms.
After revision: 1958 journal publications republished as their 1959Blackman–Tukey transformation method The method is fully described in Blackman and Tukey's book "The measurement of power spectra, from the point of view of communications engineering" and is outlined by the following procedures: Calculate the autocorrelation function with the data Apply a suitable window function, and finally Compute a discrete Fourier transform (now done with FFT) of the data to obtain the power density spectrum Autocorrelation makes the wave smoothed rather than averaging several waveforms.