Gabor expansion

which represents signal in time-frequency space

is a non-or-thogonal expansion. The nonorthogonality of the expansion causes some difficulties in the calculation of the expansion. There exist many papers concentrating on the computation aspect of the expansion. It seem that the non-locality of critical sampling Gabor expansion has not been received enough attention yet. In this paper we will show that when the window function of critical sampling Gabor expansion is continuous or symmetric

the critical sampling Gabor expansion not only can’t always truly reflect the local properties of signals

but exists convergence as well. Examples are also given.