Matthias Frank

In an ideal isotropic diffuse sound field, uncorrelated plane waves arrive uniformly from all directions. Recent theoretical work has shown that uncorrelated sources arranged on a spherical surface can also be used to synthesize diffuse fields that exhibit a uniformly vanishing active sound intensity, albeit without position-independent isotropy. How the principles extend to finite-sized rectangular cuboid and discrete source layouts remains an open question. This study considers the multi-axial superellipsoid as a flexible parametric geometry for uncorrelated acoustic source distributions. By tuning its shape parameter p, the superellipsoid transitions from an ellipsoid p=2 to a rectangular cuboid p→∞, enabling a systematic analysis of active intensity using differential geometry, Gegenbauer expansion, and numerical simulations. Findings indicate that a superellipsoidal source layer of directionally uniform density requires to be driven by a non-uniform source variance, for which a generic solution is proposed. For the ellipsoid, the proposed variance is exact and emphasizes distant sources, while for the rectangular cuboid, it remains an approximation, but still effectively emphasizes sources near edges and corners. For discrete source layouts, zero active intensity can be approximately synthesized within a domain shrunk by a factor of N/(N+1) provided that (i) sources are arranged in uniform directions of a tight spherical 2N+1 design and sample the proposed variance, or (ii) a comparable number of sources with uniform variance is distributed in a minimum potential energy configuration.

When localizing sound sources in natural or virtual environments, multisensory integration that combines auditory and visual cues is often involved. This study aims to determine the effect of (non-)individual head-related transfer functions (HRTFs) on sound source localization in the presence of visual cues. Participants (N = 16) were seated in a hemispherical loudspeaker arrangement, and their task was to indicate the perceived direction of pink-noise bursts. The conditions included localization of real loudspeakers and virtualized loudspeakers based on binaural rendering with (non-)individual HRTFs. The horizontal spacing of the visible loudspeakers was 30 degrees or larger and the vertical spacing was varied between 30 degrees and 15 degrees, to focus on vertical discrimination. The results of a static localization experiment (no head movements during playback) demonstrated an increased rate of vertical local confusions using non-individual binaural room impulse responses (BRIRs) of the KU100 dummy head compared to individual BRIRs. Dynamic auditory-visual localization with non-individual HRTFs suffered from vertical uncertainty and bias in the frontal area, where local confusion rates were consistent with the static experiment. In conclusion, the horizontal localization mapping of dynamic binaural rendering with non-individual HRTFs was comparable to real loudspeaker reproduction, while the vertical mapping was significantly impaired.

Can uncorrelated surrounding sound sources be used to generate extended diffuse sound fields? By definition, targets are a constant sound pressure level, a vanishing active sound intensity, and uncorrelated sound waves arriving isotropically from all directions. Are there ideal source layouts to synthesize a maximum diffuse sound field within? As methods, we employ numeric simulations and undertake a series of considerations based on uncorrelated source layouts at a finite radius. Statistically expected active sound intensity and sound energy density are insightful and highlight the relation of active sound intensity to potential theory. Correspondingly, both Gauß’ divergence and Newton’s spherical shell theorem apply, and they provide valuable insights. In a circular layout, uncorrelated elementary point-source fields decaying by 1/√r ideally compose an extended sound field of vanishing active sound intensity; in spherical layouts this is the case with a 1/r decay. None of the layouts synthesizes a perfectly constant sound energy density inside. Theory and simulation offer a broad basis for understanding the synthesis of diffuse sound fields with uncorrelated sources in the free sound field.

The sonification of handwriting has been shown effective in various learning tasks. In this paper, the authors investigate the sound design used for handwriting interaction based on a simple and cost-efficient prototype. The authentic interaction sound is compared with physically informed sonification designs that employ either natural or inverted mapping. In an experiment, participants copied text and drawings. The authors found simple measures of the structure-borne audio signal that showed how participants were affected in their movements, but only when drawing. In contrast, participants rated the sound features differently only for writing. The authentic interaction sound generally scored best, followed by a natural sonification mapping.

For the creation of convincing virtual acoustics of existing rooms and spaces, it is useful to apply measured Ambisonic room impulse responses (ARIRs) as a convolution reverb. Typically, tetrahedral arrays offering only first-order resolution are the preferred practical choice for measurements, because they are easily available and processed. In contrast, higher order is preferred in playback because it is superior in terms of localization accuracy and spatial clarity. There are a number of...

Singing voice directivity for five sustained German vowels /a:/, /e:/, /i:/, /o:/, /u:/ over a wide pitch range was investigated using a multichannel microphone array with high spatial resolution along the horizontal and vertical axes. A newly created dataset allows to examine voice directivity in classical singing with high resolution in angle and frequency. Three voice production modes (phonation modes) modal, breathy, and pressed that could affect the used mouth opening and voice directivity were investigated. We present detailed results for singing voice directivity and introduce metrics to discuss the differences of complex voice directivity patterns of the whole data in a more compact form. Differences were found between vowels, pitch, and gender (voice types with corresponding vocal range). Differences between the vowels /a:, e:, i:/ and /o:, u:/ and pitch can be addressed by simplified metrics up to about d2/D5/587 Hz, but we found that voice directivity generally depends strongly on pitch. Minor differences were found between voice production modes and found to be more pronounced for female singers. Voice directivity differs at low pitch between vowels with front vowels being most directional. We found that which of the front vowels is most directional depends on the evaluated pitch. This seems to be related to the complex radiation pattern of the human voice, which involves a large inter-subjective variability strongly influenced by the shape of the torso, head, and mouth. All recorded classical sung vowels at high pitches exhibit similar high directionality.

Augmented Practice Room is an e-learning tool, developed by the project team, that allows music students to practice in different acoustical environments while remaining physically in their classroom or at home. Music teachers and students from violin, ‘cello, piano, clarinet, guitar, and pop-singing classes have collaborated in testing it for a semester and giving the authors continuous feedback. In this exploratory phase, we used methods such as group discussion and semi-structured diary, with the purpose to gather as many different perspectives and reactions from participants as possible. The analysis of the collected data showed that the tool was in general positively perceived and considered useful. In particular, results merged into a four-dimensional model that describes the impact of the tool on practice: musical expressiveness, level of attention or arousal, instrument-specific technical issues, and emotional state.