International audienceARCAP time-frequency representation of narrow-band signals are madde of instantaneous characteristics (frequencies and amplitudes), without any time li,ks. In order to extract the frequency modulations (or spectral trajectoeries), we propose to re-create them on the basis of ballistic integrator models. The analytic expression of the corresponding asymptotic Kalman filter gains allows a very simple implementation of asociation procedures including trajectory birth or death. The points being associated, a Fraser filtering leads to the smoothed spectral trajectories