AES Journal

Journal of the AES

2020 June - Volume 68 Number 6


Papers

Defining Immersion: Literature Review and Implications for Research on Audiovisual Experiences

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The use of the term immersion to describe a multitude of varying experiences in the absence of a definitional consensus has obfuscated and diluted the term. The non-exhaustive literature review presented in this paper indicates that immersion is a psychological concept as opposed to being a property of the system or technology that facilitates an experience. An adaptable definition of immersion is synthesized based on the findings from the literature review: a state of deep mental in- volvement in which the individual may experience disassociation from the awareness of the physical world due to a shift in their attentional state. This definition is used to contrast and differentiate interchangeably used terms such as presence from immersion and outline the implications for conducting immersion research on audiovisual experiences. A new methodology for quantifying immersion is proposed and avenues for future work are briefly discussed.

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On the Acoustic Qualities of Dynamic Pseudo-Binaural Recordings

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The motion-tracked binaural (MTB) technique allows the dynamic, pseudobinaural rendering of spatial sound scenes recorded by a circular array of microphones on a rigid sphere. The system provides a multichannel live audio transmission from which a head-related signal with approximated interaural time and level differences can be derived and played via headphones, head tracking, and a corresponding rendering software. The latter is mainly calculating imperceptible interpolation between channel pairs during head movements. This contribution evaluates the potential of this format for the creation of virtual acoustic envi- ronments. Based on the technical realization of a 16-channel MTB array with omnidirectional diffuse field-corrected electret condenser microphone capsules, the plausibility of 8 and 16-channel recordings was tested against a physical sound source. Furthermore, the sound quality of the pseudobinaural rendering was assessed based on different items of the Spatial Audio Quality Inventory (SAQI) compared to a true dynamic binaural reference. The results show that the overall plausibility of the MTB signal with optimal interpolation is close to the reference. Even if there are small differences with respect to tone color and spatial sound source attributes, the degree of externalization and even the perceived source elevation were, despite the absence of pinna cues, well comparable to the true binaural reference.

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Perceptual Evaluation of Mitigation Approaches of Impairments due to Spatial Undersampling in Binaural Rendering of Spherical Microphone Array Data

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Spherical microphone arrays (SMAs) are widely used to capture spatial sound fields that can then be rendered in various ways as a virtual acoustic environment (VAE) including headphone-based binaural synthesis. Several practical limitations have a significant impact on the fidelity of the rendered VAE. The finite number of microphones of SMAs leads to spatial undersampling of the captured sound field, which, on the one hand, induces spatial aliasing artifacts and, on the other hand, limits the order of the spherical harmonics (SH) representation. Several approaches have been presented in the literature that aim to mitigate the perceptual impairments due to these limitations. In this article, we present a listening experiment evaluat- ing the perceptual improvements of binaural rendering of undersampled SMA data that can be achieved using state-of-the-art mitigation approaches. We examined the Magnitude Least-Squares algorithm, the Bandwidth Extraction Algorithm for Mi- crophone Arrays, Spherical Head Filters, SH Tapering, and a newly proposed equalization filter. In the experiment, subjects rated the perceived differences between a dummy head and the corresponding SMA auralization. We found that most mitiga- tion approaches lead to significant perceptual improvements, even though audible differences to the reference remain.

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Three-Halves-PowerLawModelsforActualVacuumTubes

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Presented are two new equations for three-halves-power law vacuum tube models fitted to actual devices. First, an equation involving the vacuum tube’s electrode voltages used as the variable of a polynomial that is fitted to tube amplification factor characteristics is presented. Second, a current division equation that combines grid current calculation of existing empirical formulae and caters for screen grid current at low plate voltages, a situation not handled by these, is presented. Included is an exponential function to smooth the discontinuity in plate current due to the model’s conditional treatment of grid current when tube operation moves between negative and positive control grid regions, to aid computation of derivative based tube properties such as transconductance.

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Engineering Reports

Loudspeaker and Headphone Design Approaches Enabled by Adaptive Nonlinear Control

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Traditional loudspeaker and headphone design sacrifices efficiency for sound quality. Nonlinear, adaptive control can com- pensate for undesired signal distortions, protect the transducer against overload, stabilize the voice coil position, and cope with time-varying properties of the suspension. This paper discusses the consequences of new software opportunities for designing optimum hardware components that exploit available resources, such as a nonlinear voice coil gap configuration, a softer suspension, and modal vibrations in the diaphragm, panel, and in the acoustical systems to increase the efficiency of the electroacoustical conversion. Digital signal processing (DSP) software complementing transducer hardware is the key to modern audio devices generating the required sound output with minimum size, weight, cost, and energy.

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Standards and Information Documents

AES Standards Committee News

Page: 466

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Features

Sound Exposure and Noise Pollution at Outdoor Events

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A working group of the AES Technical Committee on Acoustics and Sound Reinforcement recently published their report, "Understanding and managing sound exposure and noise pollution at outdoor events." The report is intended to present the current state of affairs surrounding the issue of outdoor event-related sound and noise. The two principal areas of investigation are sound exposure on-site and noise pollution off-site.

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Moving Air in 2020—Transducer Engineering

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Some fascinating aspects of transducer research and development were highlighted in papers and eBriefs presented at the "Virtual Vienna" convention. The overall trend was towards miniaturization, and MEMS devices come into their own here. 3D printers make it possible for experimenters to try out designs developed by others. It's also possible to develop remarkable metamaterials with specially designed resonant tube structures that enable very high levels of acoustic absorption in tiny spaces, for use in loudspeaker enclosures.

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Departments

Section News

Page: 476

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New Products

Page: 481

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Book Reviews

Page: 478

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AES Conventions and Conferences

Page: 484

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Extras

Table of Contents

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Cover & Sustaining Members List

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AES Officers, Committees, Offices & Journal Staff

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AES - Audio Engineering Society