Spatial Audio Processing: MPEG Surround and Other Applications

7.5 Single ITD approximation

In the previous experiments, the phase difference between corresponding HRTF pairs was parameterized as a frequency-dependent property. From physical considerations, it is likely that the inter-aural phase characteristic closely mimics a linear phase (delay) behavior, with some small deviations (see Figure 7.2). In the current experiment, we investigate whether the linear-phase approximation is feasible in combination with parameterized HRTF spectra. In other words, the frequency-dependent interaural phase parameters are reduced to a single inter-aural time delay (ITD) parameter for each sound source position.

7.5.1 Procedure

Given the dominance of low frequencies in ITD-based sound source localization, the ITD for a specific HRTF pair was estimated from the low-frequency part only (i.e. from 0 to 1.5 kHz). The ITD parameter was estimated by minimizing the L2 norm of the inter-aural phase error within the specified frequency range (see [202] for details). The resulting ITD was subsequently used to generate the HRTF phase spectra by computing the corresponding phase difference at the center frequencies of each parameter band. HRTF analysis and synthesis was performed using overlapping parameter bands at a fixed spectral resolution of 1 ERB (w = 1).

Since the objective of this test was to investigate potential audibility of a linear-phase approximation, no adaptive measurement procedure was employed. Instead, subjects were presented with three intervals. ...