Head-related Transfer Function Database Research Articles

Enhanced Vertical Perception through Head-Related Impulse Response Customization Based on Pinna Response Tuning in the Median Plane

Human's ability to perceive elevation of a sound and distinguish whether a sound is coming from the front or rear strongly depends on the monaural spectral features of the pinnae. In order to realize an effective virtual auditory display by HRTF (head-related transfer function) customization, the pinna responses were isolated from the median HRIRs (head-related impulse responses) of 45 individual HRIRs in the CIPIC HRTF database and modeled as linear combinations of 4 or 5 basic temporal shapes (basis functions) per each elevation on the median plane by PCA (principal components analysis) in the time domain. By tuning the weight of each basis function computed for a specific height to replace the pinna response in the KEMAR HRIR at the same height with the resulting customized pinna response and listening to the filtered stimuli over headphones, 4 individuals with normal hearing sensitivity were able to create a set of HRIRs that outperformed the KEMAR HRIRs in producing vertical effects with reduced front/back ambiguity in the median plane. Since the monaural spectral features of the pinnae are almost independent of azimuthal variation of the source direction, similar vertical effects could also be generated at different azimuthal directions simply by varying the ITD (interaural time difference) according to the direction as well as the size of each individual's own head.

Head-related transfer function database and its analyses

Based on the measurements from 52 Chinese subjects (26 males and 26 females), a high-spatial-resolution head-related transfer function (HRTF) database with corresponding anthropometric parameters is established. By using the database, cues relating to sound source localization, including interaural time difference (ITD), interaural level difference (ILD), and spectral features introduced by pinna, are analyzed. Moreover, the statistical relationship between ITD and anthropometric parameters is estimated. It is proved that the mean values of maximum ITD for male and female are significantly different, so are those for Chinese and western subjects. The difference in ITD is due to the difference in individual anthropometric parameters. It is further proved that the spectral features introduced by pinna strongly depend on individual; while at high frequencies (f ⩾ 5.5 kHz), HRTFs are left-right asymmetric. This work is instructive and helpful for the research on binaural hearing and applications on virtual auditory in future.

Customization of head-related transfer functions using principal components analysis in the time domain

Pinna responses were separated from HRIRs (head-related impulse responses) of 45 subjects in the CIPIC HRTF (head-related transfer function) database and modeled as linear combinations of five basic temporal shapes (basis functions) by PCA (principal components analysis) accounting for more than 90% of the variance in the original pinna responses per each selected elevation angle in the median plane. By adjusting the weight of each basis function computed for a specific height to replace the pinna response in the KEMAR HRIR at the same height with the resulting pinna response and listening to the filtered stimuli over headphones, four subjects were able to create a set of median HRIRs that outperformed the KEMAR HRIRs in producing elevation effects in the median plane. Since the monoaural spectral features due to the pinna are strongly dependent on elevation instead of azimuth, similar elevation effects could also be generated at different azimuthal positions simply by inserting the customized median pinna responses into the KEMAR HRIRs at other azimuths and varying the ITD (interaural time difference) according to the direction as well as the size of the subject’s own head.

A database of Head-Related Transfer Functions in whole directions on upper hemisphere.

A database of Head-Related Transfer Functions in whole directions on upper hemisphere.

A new HRTF decomposition and the corresponding algorithm for sound spatialization

Binaural simulations make extensive use of head-related transfer functions (HRTF), so spatializers have to deal with large amounts of data and long computing times to interpolate the HRTF database over the whole space. A better understanding of human auditory localization could lead to a better simulation of localization cues and allow the database and the computing time to be minimized. Principal component analysis on HRTFs, reported by D. J. Kistler and F. L. Wightman [J. Acoust. Soc. Am. 91, 1637–1647 (1992)], gave only second-order decorrelated base vectors. In order to find simple vectors (bandpass or low-pass), an independent component analysis has been computed for upper-hemisphere preprocessed HRTFs (reported in by M. Emerit et al. [Proc. 15th ICA, Trondheim, Norway, (1995) pp. 437–440]). New analyses have been done on a new HRTF data set, on different representations (time, magnitude alone and with phase). These analyses give a small number of base vectors, which can be used to reconstruct any HRTF, with a correlation coefficient near 1, and allow a new spatialization method using 3 IIR filters, derived from independent impulse responses, to be conceived. Source signals are filtered by each of these filters, and linear combination of the results gives the spatialized signal.