An exposition of joint cumulants and cumulant spectra is presented. A
distinction is emphasized in this paper between the cumulant spectrum
of a time series and its stationary version, here called a polyspectru
m. The variance and covariance of the sample bispectrum is then derive
d using a relationship between cumulant spectra of the finite Fourier
transform for the 2nd and 4th cumulant function, and the bispectrum an
d trispectrum of the time series.