A Refined Time-frequency Reassignment Technique Applied to Dolphin Echolocation Signals

Existing time-frequency representations are usually too noisesensitive or has too bad resolution for studying multiple transient signal components of biosonar signals. In this paper we calculate reassigned spectrograms using the first Hermite function as window. The optimal length Hermite function giving the perfectly localized reassignment for a Gaussian function is combined with a novel technique which includes the reassigned spectrogram using another length of the Hermite window function. For this window function the reassignment is rescaled to achieve perfect localization. The geometric mean of the two reassigned spectrograms is taken as the final estimate. The proposed method is evaluated for localization properties and noise reduction and is applied to synthetic echolocation data.