This paper describes an analysis method of nonstationary spectrum based on a modulation model. A nonstationary signal is represented by a transfer function with modulated process. Furthermore, a new spectral axis is brought to describe the nonstationarity of spectral variation. The authors proposed the instantaneous maximum entropy method (IMEM). The proposed algorithm has been applied to analyze vibration signals of the turbo charger in an automobile engine. The results of analysis by the proposed method give useful information on the delicate differences of observed signals.
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