Perceptual evaluation of filters controlling source direction: Customized and generalized HRTFs for binaural synthesis

Abstract

This paper reviews development of spatial auditory display technology based upon 20 years of research evaluating digital filters designed to spatially position auditory images associated with sound sources presented via earphones. The motivation for this review was to attempt to provide clarification regarding some of the issues and assumptions that underlie such research-driven binaural technology development. After a general discussion of research goals and methods, instructive research results are presented to underscore the main points, especially with regard to questions that could serve to stimulate further useful work of directional filter design. These include questions of how best to customize filters for individual users, and, conversely, how to optimize filters for general use. Also considered are the related questions of how best to evaluate the performance of generic Heat-Related Transfer Functions (HRTFs), in contrast to those that are measured for the use of a specific individual. At the heart of this review is a focus on the methods that are most appropriate for the evaluation of auditory imagery resulting from synthetic sound spatialization. While a primary goal for binaural synthesis is to spatially position an auditory image, methods typically employed to study the ability of human listeners to spatially localize an actual sound source address only a narrow subset of the issues that are important to the development of adequate spatial auditory display technology.