Reassigned three-dimensional phase spectrogram and ground reaction forces

The reassigned 3-dimensional phase spectrogram (R3DPS) is presented in this paper as a good candidate to exhibit instantaneous phase. It consists in coupling the reassigned power spectrogram (RS) and the phase of the short time Fourier transform (STFT). The resulting representation allows a direct observation of small phase variations in a time-frequency plane facing a phase reference. As a result, the instantaneous phase of each spectral component of a multicomponent signal can be estimated. The R3DPS allows quasi-stationary signals to be analysed. The herein objective is to detect small phase variations without loosing the energetic information given by the power spectrogram. To illustrate this method, the application to the analysis of a ground reaction forces signal is realized in order to characterize the human gait behaviour.