Sound Externalization: A Review of Recent Research

Abstract

Sound externalization, or the perception that a sound source is outside of the head, is an intriguing phenomenon that has long interested psychoacousticians. While previous reviews are available, the past few decades have produced a substantial amount of new data.In this review, we aim to synthesize those data and to summarize advances in our understanding of the phenomenon. We also discuss issues related to the definition and measurement of sound externalization and describe quantitative approaches that have been taken to predict the outcomes of externalization experiments. Last, sound externalization is of practical importance for many kinds of hearing technologies. Here, we touch on two examples, discussing the role of sound externalization in augmented/virtual reality systems and bringing attention to the somewhat overlooked issue of sound externalization in wearers of hearing aids.

On the influence of non-individual binaural cues and the impact of level normalization on auditory distance estimation of nearby sound sources

“…In the special case of distance estimation without DRR cues (anechoic) and without or only weak intensity cues, as tested in the present study, listeners might weight spectral cues more strongly than in natural acoustic conditions. Thus, whereas non-individual spectral cues do not seem to affect distance perception in more realistic listening situations [31], distance perception in our experiments under anechoic conditions was maybe affected by impaired monaural spectral cues caused by the non-individual HRTFs, similar as for example shown by Baumgartner et al [36]. Therefore, listeners may have perceived the sources closer (or to some extent less externalized) than would have been the case when using individual HRTFs.…”

“…Thus, whereas individual HRTFs improve performance especially in median plane localization, their role in distance estimation is not entirely clear [31]. This is also evident when looking at previous studies that provide contradictory results that cannot be directly attributed to the type of HRTFs used.…”

“…Zahorik showed that in reverberant conditions, the performance of distance estimation of virtual sound sources is unaffected by the use of non-individualized HRTFs compared to the use of individualized HRTFs, since the strong intensity and DRR cues mask spectral deviations [1,29,30]. In line, Begault et al [28] did not find any effects of individual HRTFs in anechoic and reverberant conditions on externalization, which is a perceptual attribute associated with distance perception [31]. Likewise, Yu et al found no evidence for an influence of individual HRTFs on distance perception of nearby sound sources [32,33].…”

Decision making in auditory externalization perception: model predictions for static conditions

“…Auditory externalization constitutes a critical aspect of spatial hearing because it can be easily disrupted when listening to sounds, e.g., via headphones or other hearing devices, that do not accurately represent the spatial properties of the listener's natural acoustic exposure [7][8][9]. Given the high prevalence of daily hearing device usage and the rapid technological advance in augmented reality systems, this topic is timely and of high social relevance.…”

Generating Artificial Reverberation via Genetic Algorithms for Real-Time Applications

“…In many cases, an audio signal is directly convolved with a Head-Related Impulse Response (HRIR) that captures only the transformations caused by the upper body of a listener to a sound in the absence of an enclosure (e.g., [ 15 ]). However, these applications can benefit from artificial reverberation, since, when the direct sound is combined with reverberation, or at least with late reflections (the tail of the reverberation), the externalization of audio sources seems to improve [ 16 ].…”