Each IMF represents a simple oscillation mode embedded in the data, which satisfies two conditions: (1) it possesses the same or nearly the same numbers of extrema and zero-crossings, and (2) it is symmetric with respect to the local zero mean. In the numerical processing, we shall demonstrate that a better resolution can be achieved for higher frequencies of the bridge if the fast Fourier transform is performed on the IMFs, rather than on the original data.