MECHANISM OF THE CROSS-TERMS IN SPECTROGRAMS

In this correspondence, using the ambiguity domain interpretation, we explore the mechanism of the cross-terms (or interferences) in spectrograms. We emphasize that the spectrogram does, in general, have cross-terms. Although being quite obvious due to the spectrogram's quadratic nature and being briefly mentioned in the literature, the occurrence and mechanism of cross-terms in spectrograms have not received much recognition so far and at least some workers in the area have been unaware of them. Depending on the signal structure and the window used, the cross-terms may sometimes by conspicuous, reduced, or completely eliminated. The cross-terms suppression in spectrograms is governed by the signal-theoretic version of the uncertainty principle. Some experimental results are provided to illustrate the cross-term mechanism in spectrograms.