Audio Signal Analysis: An Application to Wolf Population Counting

We investigate the use of signal and image theory based algorithms to estimate the number of individuals within a wolf pack howling in a given field recording, as a counting alternative to the traditional trace collecting methodologies. We, first, apply a noise-reduction signal-enhancement technique based on the numerical solving of a suitable partial differential equation acting on the spectrogram. Then, assuming that the wolves chorus may be modelled as an addition of linear chirps, we use the quadratic energy distribution corresponding to the chirplet transform of the signal to produce estimates of the corresponding instantaneous frequencies, chirp-rates and amplitudes at each instant of the recording. We finally establish suitable criteria to decide how such estimates are connected in time.