Localization of Virtual Sound Sources: Effects of Pointing Method, Visual Environment, and Training
Localization of sound sources is an important task of the human auditory system and much research effort has been put into the development of audio devices for virtual acoustics, i.e. the reproduction of spatial sounds via headphones. Even though the process of sound localization is not completely understood yet, it is possible to simulate spatial sounds via headphones by using head-related transfer functions (HRTFs). HRTFs describe the filtering of the incoming sound due to head, torso and particularly the pinna and thus they strongly depend on the particular details in the listener's geometry. In general, for realistic spatial-sound reproduction via headphones, the individual HRTFs must be measured. The currently available acoustic measurement is a technically-complex process, involves placing microphones into the listener's ears, and lasts for tens of minutes.
As a first step towards an easily accessible method for virtual acoustics, the Acoustic Research Institute visually scanned listeners' heads, obtained a geometrical representation of the heads (3-D mesh), and calculated HRTFs using numerical algorithms (part of the FWF-project P18401-B15). While their results showed that the numerical method is generally capable to calculate HRTFs, several questions remained open, especially in the interpretation from the perceptual perspective. The perceptual evaluation of the effect of the systematic parameter variation turned out to be a challenging task because of the large number of tests conditions and the lengthy psychoacoustic tests. It became clear that a sound-localization model predicting the performance is required to reduce the number of conditions for further behavioral evaluations in experiments. In LocaPhoto, we propose to develop such a sound-localization model and to continue our work on numerical HRTF calculations.
Thus the first goal of LocaPhoto is to create a functional localization model which is able to predict localization performance for sound sources positioned in 3-D free field. The model will include recent neuro-physiological findings and is aimed as a tool for further research on modeling the mechanisms behind spatial hearing by the scientific community outside of LocaPhoto.In LocaPhoto, the model will be used to evaluate HRTFs from the perceptual perspective. This will allow to achieve the second goal of LocaPhoto: the development of a method to numerically calculate perceptually valid HRTFs based on the visually retrieved geometry of a listener. Based on the results from our previous project, we plan to simplify the geometry acquisition and to increase the mesh quality by generating 3-D meshes from 2-D photos with photogrammetric-reconstruction algorithms. Given the huge amount of parameters in the numerical calculations, we expect hundreds of calculated HRTF sets. The localization model will be used to select the promising HRTF candidates, all of which will be subjectively tested in localization experiments.
While the virtual acoustics, sound-localization model and psychologigal evaluation will be performed at the Acoustic Research Institute, VRVis' will take care about the geometry acquisition stage. Existing methods for capturing the geometry of the outer ears (pinnae) and the head will be evaluated and adapted in order to find a method most applicable to this specifc field.