The present invention is concerned with the monitoring of electromechanical oscillations in electric power systems, and their identification by an adaptive algorithm based on a repeatedly measured and evaluated signal as detailed in EP-A 1 489 714. In order for an estimation of parameters of a model of the power system to reasonably converge, proper initialisation of the recursive calculation is required, including the definition of tuning parameters constraining the model and the calculation. Initialisation for a second signal to be exploited can then be simplified by copying the set of tuning parameters tuned previously for a different signal. A conditioning gain multiplying the second signal establishes compatibility between the different signals, and a signal pre-filter in turn discards contributions beyond a frequency band comprising typical electromagnetic oscillations.