Effects of Spectral Manipulation on Nonindividualized Head-Related Transfer Functions (HRTFs)

Background: Directional sounds simulated using nonindividualized head-related transfer functions (HRTFs) often result in front-back confusion. Objective: This study was designed to examine how manipulating these nonindividualized HRTF spectra can reduce front-back confusion in headphone-simulated directional sounds. Method: HRTFs of six ear-level directions were studied (angles of 0 degrees, 45 degrees, 135 degrees, 180 degrees, 225 degrees, and 315 degrees). The HRTF gains in each of six frequency bands (200 to 690 Hz, 690 to 2400 Hz, 2400 to 6500 Hz, 6500 to 10000 Hz, 10000 to 14000 Hz, and 14000 to 22000 Hz) were amplified or attenuated by 0, 12, or 18 dB. Each manipulated HRTF generated a directional sound stimulus. For this study, 32 participants were invited to localize the randomly ordered stimuli. Results: The results indicate that a 12- or 18-dB manipulation of five of the six frequency bands produced significantly better directional accuracy, with significantly less front-back confusion. A reduction of up to 70% in localization error was obtained, along with 66% less front-back confusion. Significant interactions were found between the manipulation level and frequency. Conclusion: A 12-dB spectral manipulation of selected HRTF frequency bands produces better directional accuracy. Application: The results of this research could be applied to the development of tunable nonindividualized HRTFs for audio products