Annika Neidhardt

This study investigates the plausibility of dynamic binaural audio scenarios wherein the listener interactively walks towards a virtual sound source. An originally measured BRIR set was manipulated and simplified systematically to challenge plausibility, explore its limits, and examine the relevance of selected acoustic properties. After the first investigation in a quite dry listening laboratory, this second exploratory study repeats and extends the experiment in a considerably more reverberant room. The participants had to rate externalization, continuity, stability of the apparent sound source, impression of walking towards the sound source and the plausibility of the virtual acoustic scene. The results confirm the observations of the first study in the different acoustic environment. Both studies indicate much room for simplifications, but certain modifications seriously affect plausibility. Even inexperienced listeners notice if the progress of the auditory distance change does not match their own walking motion. In addition, the meaning of context and expectation for the perception of binaural audio is highlighted.

Augmented or mixed reality (AR/MR) is emerging as one of the key technologies in the future of computing. Audio cues are critical for maintaining a high degree of realism, social connection, and spatial awareness for various AR/MR applications, such as education and training, gaming, remote work, and virtual social gatherings to transport the user to an alternate world called the metaverse. Motivated by a wide variety of AR/MR listening experiences delivered over hearables, this article systematically reviews the integration of fundamental and advanced signal processing techniques for AR/MR audio to equip researchers and engineers in the signal processing community for the next wave of AR/MR.

This study examines the plausibility of Auditory Augmented Reality (AAR) realized with position-dynamic binaural synthesis over headphones. An established method to evaluate the plausibility of AAR asks participants to decide whether they are listening to the virtual or real version of the sound object. To date, this method has only been used to evaluate AAR systems for seated listeners. The AAR realization examined in this study instead allows listeners to turn to arbitrary directions and walk towards, past, and away from a real loudspeaker that reproduced sound only virtually. The experiment was conducted in two parts. In the first part, the subjects were asked whether they are listening to the real or the virtual version, not knowing that it was always the virtual version. In the second part, the real versions of the scenes where the loudspeaker actually reproduced sound were added. Two different source positions, three different test stimuli, and two different sound levels were considered. Seventeen volunteers, including five experts, participated. In the first part, none of the participants noticed that the virtual reproduction was active throughout the different test scenes. The inexperienced listeners tended to accept the virtual reproduction as real, while experts distributed their answers approximately equally. In the second part, experts could identify the virtual version quite reliably. For inexperienced listeners, the individual results varied enormously. Since the presence of the headphones influences the perception of the real sound field, this shadowing effect had to be considered in the creation of the virtual sound source as well. This requirement still limits test methods considering the real version in its ecological validity. Although the results indicate that the availability of a hidden real reference leads to a more critical evaluation, it is crucial to be aware that the presence of the headphones slightly distorts the reference. This issue seems more vital to the plausibility estimates achieved with this evaluation method than the increased freedom in motion.

For a spatial audio reproduction in the context of augmented reality, a position-dynamic binaural synthesis system can be used to synthesize the ear signals for a moving listener. The goal is the fusion of the auditory perception of the virtual audio objects with the real listening environment. Such a system has several components, each of which help to enable a plausible auditory simulation. For each possible position of the listener in the room, a set of binaural room impulse responses (BRIRs) congruent with the expected auditory environment is required to avoid room divergence effects. Adequate and efficient approaches are methods to synthesize new BRIRs using very few measurements of the listening room. The required spatial resolution of the BRIR positions can be estimated by spatial auditory perception thresholds. Retrieving and processing the tracking data of the listener’s head-pose and position as well as convolving BRIRs with an audio signal needs to be done in real-time. This contribution presents work done by the authors including several technical components of such a system in detail. It shows how the single components are affected by psychoacoustics. Furthermore, the paper also discusses the perceptive effect by means of listening tests demonstrating the appropriateness of the approaches.

It is pointed out that beyond reproducing the physically correct sound pressure at the eardrums, more effects play a significant role in the quality of the auditory illusion. In some cases, these can dominate perception and even overcome physical deviations. Perceptual effects like the room-divergence effect, additional visual influences, personalization, pose and position tracking as well as adaptation processes are discussed. These effects are described individually, and the interconnections between them are highlighted. With the results from experiments performed by the authors, the perceptual effects can be quantified. Furthermore, concepts are proposed to optimize reproduction systems with regard to those effects. One example could be a system that adapts to varying listening situations as well as individual listening habits, experience and preference.