Abstract
The head-related transfer function (HRTF) defines the acoustic path from a source to the two ears of a listener in a manner that is highly dependent on direction. This directional dependence arises from the highly individual morphology of the pinna, which results in complex reflections and resonances. While this notion is generally accepted, there has been little research on the importance of different structural elements of the pinna on the HRTF. A parametric three-dimensional ear model was used to investigate the changes in shape of the pinna in a systematic manner with a view to determining important contributing morphological parameters that can be used for HRTF individualization. HRTFs were simulated using the boundary element method. The analysis comprised objective comparisons between the directional transfer function and diffuse field component. The mean spectral distortion was used for global evaluation of HRTF similarity across all simulated positions. A perceptual localization model was used to determine correspondences between perceptual cues and objective parameters. A reasonable match was found between the modelled perceptual results and the mean spectral distortion. Modifications to the shape of the concha were found to have an important impact on the HRTF, as did those in proximity to the triangular fossa. Furthermore, parameters that control the relief of the pinna were found to be at least as important as more frequently cited side-facing parameters, highlighting limitations in previous morphological/HRTF studies.
Highlights
The head-related transfer function (HRTF) defines the acoustic path from a source to the two ears of a listener in a manner that is highly dependent on direction
Rather than focusing directly on the impact of changes to the CIPIC parameters, this study investigates the effect of morphological changes by moving specific control points, many of which are linked to the CIPIC parameters
The reference and CP3-max exhibit only a single, prominent notch in this frequency range. Considering that this is only one single slice of the full spatial parameter space, it highlights the difficulty of a spatio-frequency analysis over the large number of pinna variations with the aim of finding the most pertinent control points. While this type of investigation is an interesting avenue to explore, it is outside the scope of this study, and analysis will be restricted to the global spectral distortion (SD) measure defined in Sec
Summary
The head-related transfer function (HRTF) defines the acoustic path from a source to the two ears of a listener in a manner that is highly dependent on direction. This directional dependence arises from the highly individual morphology of the pinna, which results in complex reflections and resonances. Listening to a spatial sound scene using a HRTF, one’s own or that from another individual, is achieved using binaural synthesis This technique processes a monophonic sound source by the left and right ear filters corresponding to the desired source direction (e.g., Poirier-Quinot and Katz, 2018). It is possible to adapt to non-individual HRTFs (Carlile et al, 2014; Hofman et al, 1998; Parseihian and Katz, 2012; Poirier-Quinot and Katz, 2020), but this can be very dependent on the individual, with some unable to adapt even after repeated exposure to training (Stitt et al, 2019; Trapeau et al, 2016)
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