Florian Klein

How we perceive and remember room acoustics is of particular interest in the domain of spatial audio. For the creation of virtual or augmented acoustic environments, a room acoustic impression needs to be created which matches the expectations of certain room classes or a specific room. These expectations are based on the auditory memory of the acoustic room impression. In this paper, we present an exploratory study to evaluate the ability of listeners to remember specific rooms. The task of the listeners was to detect the reference room in a modified ABX double-blind stimulus test which featured a pre-defined playback order and a fixed time schedule. Furthermore, we explored distraction effects by employing additional non-acoustic interferences. The results show a significant decrease of the auditory memory capacity within ten seconds, which is more pronounced when the listeners were distracted. However, the results suggest that auditory memory depends on what auditory cues are available.

For the realization of auditory augmented reality (AAR), it is important that the room acoustical properties of the virtual elements are perceived in agreement with the acoustics of the actual environment. This perceptual matching of room acoustics is the subject reviewed in this paper. Realizations of AAR that fulfill the listeners? expectations were achieved based on pre-characterization of the room acoustics, for example, by measuring acoustic impulse responses or creating detailed room models for acoustic simulations. For future applications, the goal is to realize an online adaptation in (close to) real-time. Perfect physical matching is hard to achieve with these practical constraints. For this reason, an understanding of the essential psychoacoustic cues is of interest and will help to explore options for simplifications. This paper reviews a broad selection of previous studies and derives a theoretical framework to examine possibilities for psychoacoustical optimization of room acoustical matching.

In binaural rendering, the room divergence effect refers to the decrease in perceived externalization due to a mismatch between the room acoustics of the virtual sounds and those of the listening space. However, it is currently unknown which specific acoustic differences cause this effect. In this work, we present a pilot study to determine detection thresholds between sound sources recorded under different acoustic conditions in a variable acoustics room. These results are intended to predict situations where divergence effects can be expected. The participants had to perform a triangle test where they could listen to three sound sources placed at different positions in the room. The test design was motivated by the fact that sound sources are not placed at the same position in real acoustic scenes. One sound source was recorded under different acoustic conditions than the other two, and the task for the participant was to detect the differing source. The test was conducted in the measured room using 3 DoF binaural reproduction and using a virtual reality (VR) headset to display a visual 360 capture of the room enabling the subjects to see the positions of the sources in the room. Detection rates are signal-dependent and increase with differences in reverberation time (RT). For the most critical signal in the test (castanets), an RT difference of 8% was detectable, while the difference was 15% across all conditions. Furthermore, we discuss the influence of sound source distance and absorption configuration (symmetric or asymmetric) on detection thresholds.

Parametric spatial audio rendering is a popular approach for low computing capacity applications, such as augmented reality systems. However most methods rely on spatial room impulse responses (SRIR) for sound field rendering with 3 degrees of freedom (DoF), i.e., for arbitrary head orientations of the listener, and often require multiple SRIRs for 6-DoF rendering, i.e., when additionally considering listener translations. This paper presents a method for parametric spatial audio rendering with 6 DoF based on one monaural room impulse response (RIR). The scalable and perceptually motivated encoding results in a parametric description of the spatial sound field for any listener's head orientation or position in space. These parameters form the basis for the binaural room impulse responses (BRIR) synthesis algorithm presented in this paper. The physical evaluation revealed good performance, with differences to reference measurements at most tested positions in a room below the just-noticeable differences of various acoustic parameters. The paper further describes the implementation of a 6-DoF realtime virtual acoustic environment (VAE) using the synthesized BRIRs. A pilot study assessing the plausibility of the 6-DoF VAE showed that the system can provide a plausible binaural reproduction, but it also revealed challenges of 6-DoF rendering requiring further research.

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.