An innovative Hilbert ndash;Huang transform (HHT) based frequency identification approach designated as adaptive magnitude spectrum algorithm(AMSA) is proposed in this paper. Characterized by the a posteriori property, the AMSA does not need the a priori information about the modalfrequencies to be identified, and the situations that a modal frequency may be contained along specific segments of the whole time duration ofone or more intrinsic mode functions (IMFs) are allowed for automatically ...