Christian Schneiderwind

In order to successfully fuse virtual sound sources with the real acoustic environment, the acoustic properties of the real environment must be estimated and utilized for the synthesis of virtual sound sources. Often, just noticeable differences (JNDs) of room acoustic parameters are utilized to predict a good match between virtual and real acoustics. However, several studies in this domain have shown that existing JND values of room acoustic parameters are often not able to predict the perception of the listeners. This can have various reasons: Differences in first reflection patterns are barely measurable with classical acoustic parameters; Even if acoustic differences are above the JND, a plausible reproduction might still be possible; JNDs depend on various factors (such as sound signal, etc.) and existing studies do not cover all of them. The last factor is addressed in this research paper. A three-alternative forced (3AFC) choice test was conducted at four different loudness levels (75 dB(A), 65 dB(A), 55 dB(A), and 45 dB(A)) in a reverberation time range from 0.5 s to 0.8 s. A dependency of the loudness on the detectability of reverberation differences was found for the randomly interleaved presentation of loudness levels but not for sequential presentation. Individual hearing thresholds as well as expertise level significantly influence the JND of reverberation time.

This exploratory study investigates peoples’ ability to discriminate between real and virtual sound sources in a position-dynamic headphone based augmented audio scene. For this purpose, an acoustic scene was created consisting of two loudspeakers at different positions in a small seminar room. Considering the presence of headphones, non-individualized BRIRs measured along a line with a dummy head wearing AKG K1000 headphones were used to allow for head rotation and translation. In a psychoacoustic experiment, participants had to explore the acoustic scene and tell which sound source they believe is real or virtual. The test cases included a dialog scenario, stereo pop-music and one person speaking while the other speaker played mono-music simultaneously. Results show that the participants were on trend able to debunk individual virtual sources. However, for the cases where both sound sources reproduced sound simultaneously, lower distinguishability rates were observed.

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.

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.