Numerical study on source-distance dependency of head-related transfer functions

Area of Science:

• Acoustics
• Bioacoustics
• Auditory Neuroscience

Background:

• Head-related transfer functions (HRTFs) are crucial for spatial audio perception.
• Understanding how HRTFs change with source distance is vital for realistic 3D audio.
• Previous research indicates HRTF spectral features vary with source distance.

Purpose of the Study:

• To investigate the source-distance dependency of HRTFs on horizontal and median sagittal planes.
• To elucidate the role of the outer ear's angle of incidence in HRTF distance variations.
• To differentiate the influence of the outer ear and head presence on HRTF distance effects.

Main Methods:

• Utilized the boundary-element method for HRTF calculations.
• Employed a dummy head scanned via laser and computed tomography.
• Compared HRTF spectra in both head-centered and ear-centered coordinate systems.

Main Results:

• HRTF spectra confirm variations with source distance, consistent with prior studies.
• Ear-centered analysis highlights the outer ear's angle of incidence as key for ipsilateral HRTF distance dependency.
• Contralateral HRTFs are primarily influenced by the head's presence.
• Ipsilateral HRTFs show minimal distance dependency beyond 0.2m (ear-centered); contralateral HRTFs up to 1.8m.
• HRTFs on the median sagittal plane are sensitive to distances within 0.4m.

Conclusions:

• The outer ear's angle of incidence significantly impacts ipsilateral HRTF distance dependency on the horizontal plane.
• The head's presence is the main factor for contralateral HRTF distance variation.
• Defined distance thresholds for HRTF independence in different planes and ear-centered perspectives.