This Topic extends the definition of the power-spectral density in two ways. First, it considers the cross-power spectral density (CPSD) for considering the spectral characteristics of two-jointly stationary processes. It takes the natural definition of being the Discrete-Time Fourier Transform (DTFT) of the cross-correlation function. The video considers some relevant properties of the CPSD. The Topic then considers that, due to technical limitations of the DTFT, taking the bilateral z-transform of the auto- or cross-correlation sequences is a more powerful technique. This is defined as the complex- and cross-complex spectral densities. An example of the complex-spectral density is calculated. Finally, a discussion of using z-transform tables for taking inverse transforms is provided.