The Spectra of Digitally Encoded Video Signals

Because of the nonlinear nature of quantizing and coding operations, it is not possible, in general, to derive the power spectrum for a digitally encoded signal from a knowledge of only the spectrum of the original analog signal. For video signals, however, the analog process can be modeled by the random step function. This leads to a convenient expression for the power spectral density of the digital signal with separate factors characterizing the effects of 1) digital pulse shape, 2) quantizing and coding operations, 3) scanning raster, and 4) the bandwidth of the analog signal. Experimental data from television and Picturephone® signals are presented. The results are of special significance to a hybrid analog-digital system.