Background In order to present virtual sound sources via headphones spatially, head-related transfer functions (HRTFs) can be applied to audio signals. In this so-called binaural virtual acoustics, the spatial perception may be degraded if the HRTFs deviate from the true HRTFs of the listener. Objective In this study, participants wearing virtual reality (VR) headsets performed a listening test on the 3D audio perception of virtual audiovisual scenes, thus enabling us to investigate the necessity and influence of the individualization of HRTFs. Two hypotheses were investigated: first, general HRTFs lead to limitations of 3D audio perception in VR and second, the localization model for stationary localization errors is transferable to nonindividualized HRTFs in more complex environments such as VR. Methods For the evaluation, 39 subjects rated individualized and nonindividualized HRTFs in an audiovisual virtual scene on the basis of 5 perceptual qualities: localizability, front-back position, externalization, tone color, and realism. The VR listening experiment consisted of 2 tests: in the first test, subjects evaluated their own and the general HRTF from the Massachusetts Institute of Technology Knowles Electronics Manikin for Acoustic Research database and in the second test, their own and 2 other nonindividualized HRTFs from the Acoustics Research Institute HRTF database. For the experiment, 2 subject-specific, nonindividualized HRTFs with a minimal and maximal localization error deviation were selected according to the localization model in sagittal planes. Results With the Wilcoxon signed-rank test for the first test, analysis of variance for the second test, and a sample size of 78, the results were significant in all perceptual qualities, except for the front-back position between own and minimal deviant nonindividualized HRTF (P=.06). Conclusions Both hypotheses have been accepted. Sounds filtered by individualized HRTFs are considered easier to localize, easier to externalize, more natural in timbre, and thus more realistic compared to sounds filtered by nonindividualized HRTFs.

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Human listeners need to permanently interact with their threedimensional (3-D) environment. To this end, they require efficient perceptual mechanisms to form a sufficiently accurate 3-D auditory space.In this chapter, we discuss the formation of the 3-D auditory space from various perspectives. The aim is to show the link between cognition, acoustics, neurophysiology, and psychophysics, when it comes to spatial hearing. First, we present recent cognitive concepts for creating internal models of the complex auditory environment. Second, we describe the acoustic signals available at our ears and discuss the spatial information they convey. Third, we look into neurophysiology, seeking for the neural substrates of the 3-D auditory space. Finally, we elaborate on psychophysical spatial tasks and percepts that are possible just because of the formation of the auditory space.

In this article, we present the current state of the art in binaural audio with the focus on head-related transfer functions (HRTFs) and valuation methods of virtual acoustics with descriptive attributes. This combination provides a methodology, which delivers the basis for research studies in virtual reality (VR) on individual and non-individual head-related transfer functions. Based on the largely explored localization perception of static audio signals, this review offers an overview of the directional hearing during head and sound source movement and multimodality in audiovisual virtual environments. Perceptual quality characteristics provide evaluation methods from which future HRTF VR experiments and virtual environments studies on binaural acoustics could benefit.