Toward Sound Localization Testing in Virtual Reality to Aid in the Screening of Auditory Processing Disorders.

Sound localization testing is key for comprehensive hearing evaluations, particularly in cases of suspected auditory processing disorders. However, sound localization is not commonly assessed in clinical practice, likely due to the complexity and size of conventional measurement systems, which require semicircular loudspeaker arrays in large and acoustically treated rooms. To address this issue, we investigated the feasibility of testing sound localization in virtual reality (VR). Previous research has shown that virtualization can lead to an increase in localization blur. To measure these effects, we conducted a study with a group of normal-hearing adults, comparing sound localization performance in different augmented reality and VR scenarios. We started with a conventional loudspeaker-based measurement setup and gradually moved to a virtual audiovisual environment, testing sound localization in each scenario using a within-participant design. The loudspeaker-based experiment yielded results comparable to those reported in the literature, and the results of the virtual localization test provided new insights into localization performance in state-of-the-art VR environments. By comparing localization performance between the loudspeaker-based and virtual conditions, we were able to estimate the increase in localization blur induced by virtualization relative to a conventional test setup. Notably, our study provides the first proxy normative cutoff values for sound localization testing in VR. As an outlook, we discuss the potential of a VR-based sound localization test as a suitable, accessible, and portable alternative to conventional setups and how it could serve as a time- and resource-saving prescreening tool to avoid unnecessarily extensive and complex laboratory testing.

Phoneme dependence of horizontal asymmetries in voice directivity.

Human voice directivity shows horizontal asymmetries caused by the shape of the lips or the position of the tooth and tongue during vocalization. This study presents and analyzes the asymmetries of voice directivity datasets of 23 different phonemes. The asymmetries were determined from datasets obtained in previous measurements with 13 subjects in a surrounding spherical microphone array. The results show that asymmetries are inherent to human voice production and that they differ between the phoneme groups with the strongest effect on the [s], the [l], and the nasals [m], [n], and [ŋ]. The least asymmetries were found for the plosives.

Investigating phoneme-dependencies of spherical voice directivity patterns II: Various groups of phonemes.

The substantial variation between articulated phonemes is a fundamental feature of human voice production. However, while the spectral and temporal aspects of the phonemes have been extensively studied, few have investigated the spatial aspects and analyzed phoneme-dependent differences in voice directivity. This paper extends our previous research focusing on the directivity patterns of selected vowels and fricatives [Pörschmann and Arend, J. Acoust. Soc. Am. 149(6), 4553-4564 (2021)] and examines different groups of phonemes, such as plosives, nasals, voiced alveolars, and additional fricatives. For this purpose, full-spherical voice directivity measurements were performed for 13 persons while they articulated the respective phonemes. The sound radiation was recorded simultaneously using a surrounding spherical microphone array with 32 microphones and then spatially upsampled to a dense sampling grid. Based on these upsampled datasets, the spherical voice directivity was studied, and phoneme-dependent variations were analyzed. The results show significant differences between the groups of phonemes. However, within three groups (plosives, nasals, and voiced alveolars), the differences are small, and the variations in the directivity index were statistically insignificant.

Effects of hand postures on voice directivity.

While speaking, hand postures, such as holding a hand in front of the mouth or cupping the hands around the mouth, influence human voice directivity. This study presents and analyzes spherical voice directivity datasets of an articulated [a] with and without hand postures. The datasets were determined from measurements with 13 subjects in a surrounding spherical microphone array with 32 microphones and then upsampled to a higher spatial resolution. The results show that hand postures strongly impact voice directivity and affect the directivity index by up to 6 dB, which is more than variances caused by phoneme-dependent differences.

Binaural reproduction of dummy head and spherical microphone array data-A perceptual study on the minimum required spatial resolution.

Dynamic binaural synthesis requires binaural room impulse responses (BRIRs) for each head orientation of the listener. Such BRIRs can either be measured with a dummy head or calculated from the spherical microphone array (SMA) data. Because the dense dummy head measurements require enormous effort, alternatively sparse measurements can be performed and then interpolated in the spherical harmonics domain. The real-world SMAs, on the other hand, have a limited number of microphones, resulting in spatial undersampling artifacts. For both of the methods, the spatial order N of the underlying sampling grid influences the reproduction quality. This paper presents two listening experiments to determine the minimum spatial order for the direct sound, early reflections, and reverberation of the dummy head or SMA measurements required to generate the horizontally head-tracked binaural synthesis perceptually indistinguishable from a high-resolution reference. The results indicate that for direct sound, N = 9-13 is required for the dummy head BRIRs, but significantly higher orders of N = 17-20 are required for the SMA BRIRs. Furthermore, significantly lower orders are required for the late parts with N = 4-5 for the early reflections and reverberation of the dummy head BRIRs but N = 12-13 for the early reflections and N = 6-9 for the reverberation of the SMA BRIRs.

Investigating phoneme-dependencies of spherical voice directivity patterns.

Dynamic directivity is a specific characteristic of the human voice, showing time-dependent variations while speaking or singing. To study and model the human voice's articulation-dependencies and provide datasets that can be applied in virtual acoustic environments, full-spherical voice directivity measurements were carried out for 13 persons while articulating eight phonemes. Since it is nearly impossible for subjects to repeat exactly the same articulation numerous times, the sound radiation was captured simultaneously using a surrounding spherical microphone array with 32 microphones and then subsequently spatially upsampled to a dense sampling grid. Based on these dense directivity patterns, the spherical voice directivity was studied for different phonemes, and phoneme-dependent variations were analyzed. The differences between the phonemes can, to some extent, be explained by articulation-dependent properties, e.g., the mouth opening size. The directivity index, averaged across all subjects, varied by a maximum of 3 dB between any of the vowels or fricatives, and statistical analysis showed that these phoneme-dependent differences are significant.

Impact of face masks on voice radiation.

With the COVID-19 pandemic, the wearing of face masks covering mouth and nose has become ubiquitous all around the world. This study investigates the impact of typical face masks on voice radiation. To analyze the transmission loss caused by masks and the influence of masks on directivity, this study measured the full-spherical voice directivity of a dummy head with a mouth simulator covered with six masks of different types, i.e., medical masks, filtering facepiece respirator masks, and cloth face coverings. The results show a significant frequency-dependent transmission loss, which varies depending on the mask, especially above 2 kHz. Furthermore, the two facepiece respirator masks also significantly affect speech directivity, as determined by the directivity index (DI). Compared to the measurements without a mask, the DI deviates by up to 7 dB at frequencies above 3 kHz. For all other masks, the deviations are below 2 dB in all third-octave frequency bands.