On the externalization of virtual sound images in headphone reproduction: A Wiener filter approach

Abstract

In-head localization of sound images is a critical problem in headphone reproduction. The paper investigates the degree of externalization in terms of the distance of auditory images for various synthesis and reproduction cases. An effective binaural headphone system was constructed by way of binaural synthesis using head-related impulse responses and individual headphone equalization using Wiener filter theory. The headphone system designed had an average reproduction performance error of 2.4% for five subjects with a random noise input, and was used to perform some subjective tests with a set of virtual sources equally spaced and distanced from the center of each subject's head in the horizontal plane. The effects of individual and nonindividual binaural syntheses and those of equalized and nonequalized reproductions were separately investigated. In the tests, each subject was instructed to indicate the distance of auditory images. The results obtained demonstrate that individual equalization is important for externalization, and individual synthesis is important for consistent distance perception. Thus, a combined use of both individual equalization and individual synthesis resulted in externalized sound images of a consistent distance.

Influence of head tracking on the externalization of speech stimuli for non-individualized binaural synthesis

“…According to Hartmann and Wittenberg (1996), the synthesis of a distant source leads to a perfectly externalized image if the HRTFs are properly individualized, whereas it leads to an image that is often perceived on the surface of the skull if the HRTFs are non-individualized. With five subjects and short bursts of white noise reproduced in the horizontal plane, Kim and Choi (2005) observed that sound sources synthesized with individualized HRTFs were perceived at a greater and more consistent distance than those synthesized with non-individualized HRTFs. On the other hand, with speech stimuli, neither Møller et al (1996) nor Begault et al (2001) reported a significant difference in externalization between individualized and non-individualized binaural synthesis.…”

“…Using virtual sources synthesized in the horizontal plane with non-individualized HRTFs and no head tracking, Laws and Platte (1975), Kim and Choi (2005), and Begault and Wenzel (1993) observed that lateral stimuli were almost always judged to be external, whereas frontal or rear stimuli were much more likely to be perceived inside the head. Note that Begault and Wenzel (1993) used anechoic speech stimuli.…”

“…The scale was inspired by several previous studies (Hartmann and Wittenberg, 1996;Kim and Choi, 2005;Kawaura et al, 1991;Boyd et al, 2012). Once subjects had given their answer, the next stimulus was automatically played.…”

Binaural technology for virtual reality

“…It is difficult, due to the high variability, to obtain one filter characteristic which is valid generally for all users [KC00]. The externalization of virtual sound images without additional signal processing in headphone reproduction is often a problematic issue, too [KC05].…”

A preliminary study on spatial unmasking of virtual separated sources

“…This leads to some shortcomings in studying forward masking with loudspeakers for their transient properties, at least those having short delay time. However, eliminating the effect of inside-the-head localization is essential when studying spatial unmasking with headphones [10,11] .…”