Glossary of Sleep-related terms

Spectrum ("power" spectrum)

A function of frequency showing the "power" (actually, the squared voltage) of a segment of record, in each of many frequency ranges. It can be calculated at a discrete set of frequencies, as the Fourier Transform of the segment's autocorrelation function, or as sums of squares of the Fourier transform of the segment itself (in between the discrete frequencies, it can be estimated by quadratic interpolation).4