In binaural signals, interaural time differences (ITDs) and interaural level differences (ILDs) are two of the most important cues for the estimation of source azimuths, i.e. the localization of sources in the horizontal plane. For narrow band signals, according to the duplex theory, ITD is dominant at low frequencies and ILD is dominant at higher frequencies. Based on the STFT spectra of binaural signals, a method is proposed for the combined evaluation of ITD and ILD for each individual spectral coefficient. ITD and ILD are related to the azimuth through lookup models. Azimuth estimates based on ITD are more accurate but ambiguous at higher frequencies due to phase wrapping. The less accurate but unambiguous azimuth estimates based on ILDs are used in order to select the closest candidate azimuth estimates based on ITDs, effectively improving the azimuth estimation. The method corresponds well with the duplex theory and also handles the transition from low to high frequencies gracefully. The relations between the ITD and ILD and the azimuth are computed from a measured set of head related transfer functions (HRTFs), yielding azimuth lookup models. Based on a study of these models for different subjects, parametric azimuth lookup models are proposed. The parameters of these models can be optimized for an individual subject whose HRTFs have been measured. In addition, subject independent lookup models are proposed, parametrized only by the distance between the ears, effectively enabling source localization for subjects whose HRTFs have not been measured.

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