A continuous, functional representation of a large set of head-related transfer function measurements ͑HRTFs͒ is developed. The HRTFs are represented as a weighted sum of surface spherical harmonics ͑SSHs͒ up to degree 17. A Gaussian quadrature method is used to pick out a set of experimentally efficient measurement directions. Anechoic impulse responses are measured for these directions between a source loudspeaker and the entrance to the ear canal of a head-and-torso simulator ͑HATS͒. Three separate SSH analyses are carried out: The first forms a SSH representation from the time responses, with the variable onset delay caused by interaural differences intact, by applying the analysis to each time sample in turn. The second SSH model is formed in exactly the same way, except using impulse responses in which the variable onset delays have been equalized. The final SSH analysis is carried out in the frequency domain by applying the technique on a frequency bin by frequency bin basis to the magnitude and unwrapped phase responses of the HRTFs. The accuracy and interpolation performance of each of the computed SSH models is investigated, and the usefulness of the SSH technique in analyzing directional hearing and, particularly, in spatializing sounds is discussed.

This paper introduces the process for creating the Sydney York Morphological and Acoustic Recordings of Ears (SYMARE) database. The SYMARE database supports research exploring the relationship between the morphology of human outer ears and their acoustic filtering properties-a relationship that is viewed by many as holding the key to human spatial hearing and the future of 3D personal audio. The SYMARE database is comprised of acoustically measured head-related impulse responses for 61 listeners (48 male/13 female), multiple high-resolution surface mesh models (upper torso, head and ears) for these listeners obtained from magnetic resonance imaging (MRI) data, and the corresponding simulated HRIR data for these listeners generated using the Fast Multipole Boundary Element Method (FM-BEM). In this work, we compare acoustically measured HRIR data for 61 listeners with the listeners' corresponding simulated HRIR data generated using the FM-BEM.Index Terms-Fast multipole boundary element method, head-related transfer function, morphological data, virtual auditory space, 3D audio, 3D mesh models. Manuscript

When validating systems that use headphones to synthesize virtual sound sources, a direct comparison between virtual and real sources is sometimes needed. This paper considers the passive influence of headphones on the sound transmission and perception of external loudspeaker sources, for which physical measurements and behavioral data have been obtained. Physical measurements of the effect of a number of headphone models are given and analyzed using an auditory filter bank and binaural cue extraction. These highlighted that all of the headphones had an effect on localization cues and repositioning had a measurable effect. A localization test was undertaken using one of the best performing headphones from the measurements. It was found that the presence of the headphones caused a small increase in localization error and that the process of judging source location was different, highlighting a possible increase in the complexity of the localization task. INTRODUCTIONThe use of binaural rendering is popular in a number of audio applications-from hearing research [1-3] to entertainment [4,5]. In each application, the specific requirements for the performance of a binaural system will be slightly different although generally, the aim is to induce the perception of intended auditory events as accurately as possible. Designing an assessment methodology that validates a binaural system within its intended application is often a difficult task. A common metric for a binaural system is the ability to produce a virtual sound source that is indistinguishable from a real sound source. Indirect comparisons have been investigated, for example, by Minnaar et al. [6] and Møller et al. [7,8] in which non-dynamic binaural simulation and real loudspeaker localization tasks were considered in separated experiments. However, for direct comparisons where real and virtual loudspeakers are presented simultaneously, the validation of headphone-based binaural systems against a real loudspeaker reference can be problematic. The listener must wear the headphones throughout the experiment, which will affect the sound transmission from the external loudspeakers. A number of discrimination studies have involved direct comparison of real sources with headphone-delivered virtual sources [9-13] as well as some recent localization tests [14,15] and loudness equalization studies [16,17]. The passive use of headphones may have a significant effect on the perception of the external loudspeaker and therefore cause an unknown and possibly directionally dependent bias. Hartmann and Wittenberg [10] noted that wearing headphones appeared to affect the listeners' ability to distinguish between front and back, although they also state that they were not aware of its effect on experiments in the azimuthal plane. To highlight the importance of the problem, Erbes et al.[18] presented work on the development of an advanced headphone system specifically for the field of binaural reproduction.This study investigates whether headphones mounted on a listener will ...

International audienc

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