Continuous-direction model of the broadband time-of-arrival in the head-related transfer functions

Head-related transfer functions (HRTFs) describe the filtering of the incoming sound by the human anatomy. They contain the so-called broadband time-of-arrivals (TOAs), which interaural differences yield the well-known interaural time differences used to estimate the lateral position of sound sources by the human auditory system. The TOAs are essential for a time-synchronous binaural rendering of multiple virtual sound sources or for interpolation of the timing information in an existing HRTF set. Estimation of the TOA is usually done separately for each spatial direction, and is thus, prone to errors and directional outliers. A method for a robust estimation of a continuous-direction TOA function from a set of listener-specific HRTFs is presented. The method relies on a geometric model of the HRTF-measurement setup represented by parameters like head position, radius, and ear position. The model parameters were fit to HRTFs of a sphere numerically calculated under various conditions. The resulting model parameters and TOA functions corresponded well to the measurement geometry and manually derived TOAs, respectively. The model was further evaluated in a setup assuming a listener placed off-axis in the HRTF-measurement setup, demonstrating the potential impact of the usually neglected aspect of listener position on the modeling results.