Morphoacoustic perturbation analysis: principles and validation

We present a frequency domain technique for investigating the relationship between acoustic properties of the human hearing system and the morphology responsible for creating them. Exploiting reciprocity, the boundary element method is applied to determine head-related transfer functions (HRTFs) for various directions and distances from a surface mesh model of a head and pinnae. Small orthogonal surface harmonic deformations are applied to the mesh one at a time and stored in a database together with the resulting, approximately linear, changes to the HRTFs (delta HRTFs). Once the computationally intensive process of constructing the database has been completed, identifying the morphological origins of arbitrary acoustic spectral features is very rapid. The method, which we term morphoacoustic perturbation analysis in the frequency domain (MPA-FD), is outlined and a proof-of-principle implementation described. MPA-FD is demonstrated by using it to determine the regions of the pinna responsible for determining the centre frequency of an HRTF notch and a peak. The predictions show good agreement with direct acoustic measurements.