AES Munich 2009
Paper Session P16
Spatial Rendering–Part 1
Saturday, May 9, 09:00 — 11:30
Chair: Andreas Silzle
P16-1 An Alternative Ambisonics Formulation: Modal Source Strength Matching and the Effect of Spatial Aliasing—Franz Zotter, Hannes Pomberger, University of Music and Dramatic Arts - Graz, Austria; Matthias Frank, Graz University of Technology - Graz, Austria
Ambisonics synthesizes sound fields as a sum over angular (spherical/cylindrical harmonic) modes, resulting in the definition of an isotropically smooth angular resolution. This means, virtual sources are synthesized with outstanding smoothness across all angles of incidence, using discrete loudspeakers that uniformly cover a spherical or circular surface around the listening area. The classical Ambisonics approach models the fields of these discrete loudspeakers in terms of a sampled continuum of plane-waves. More accurately, the contemporary concept of Ambisonics uses a continuous angular distribution of point-sources at finite distance instead, which is considerably easier to imagine. This also improves the accuracy of holophonic sound field synthesis and the analytic description of the sweet spot. The sweet spot is a limited area of faultless synthesis emerging from angular harmonics truncation. Additionally, playback with loudspeakers causes spatial aliasing. In this sense, it allows for a successive consideration of the major shortcomings of Ambisonics: the limited sweet spot size and spatial aliasing. To elaborate on this concept this paper starts with the solution of the nonhomogeneous wave equation for a spherical point-source distribution, and ends with a novel study on spatial aliasing in Ambisonics.
Convention Paper 7740 (Purchase now)
P16-2 Sound Field Reproduction Employing Non-Omnidirectional Loudspeakers—Jens Ahrens, Sascha Spors, Deutsche Telekom Laboratories, Techniche Universität Berlin - Berlin, Germany
In this paper we treat sound field reproduction via circular distributions of loudspeakers. The general formulation of the approach has been recently published by the authors. In this paper we concentrate on the employment of secondary sources (i.e., loudspeakers) whose spatio-temporal transfer function is not omnidirectional. The presented approach allows us to treat each spatial mode of the secondary source’s spatio-temporal transfer function individually. We finally outline the general process of incorporating spatio-temporal transfer functions obtained from microphone array measurements.
Convention Paper 7741 (Purchase now)
P16-3 Alterations of the Temporal Spectrum in High-Resolution Sound Field Reproduction of Different Spatial Bandwidths—Jens Ahrens, Sascha Spors, Deutsche Telekom Laboratories, Techniche Universität Berlin - Berlin, Germany
We present simulations of the wave field reproduced by a discrete circular distribution of loudspeakers. The loudspeaker distribution is driven either with signals of infinite spatial bandwidth (as it happens in wave field synthesis), or the loudspeaker distribution is driven with signals of finite spatial bandwidth (as it is the case in near-field compensated higher order Ambisonics). The different spatial bandwidths lead to different accuracies of the desired component of the reproduced wave field and to spatial aliasing artifacts with essentially different properties. Our investigation focuses on the potential consequences of the artifacts on human perception.
Convention Paper 7742 (Purchase now)
P16-4 Cooperative Spatial Audio Authoring: Systems Approach and Analysis of Use Cases—Jens-Oliver Fischer, Fraunhofer Institute for Digital Media Technology IDMT - Ilmenau, Germany; Francis Gropengiesser, TU Ilmenau - Ilmenau, Germany; Sandra Brix, Fraunhofer Institute for Digital Media Technology IDMT - Ilmenau, Germany
Today’s audio production process is highly parallel and segregated. This is especially the case in the field of audio postproduction for motion pictures. The introduction of spatial audio systems like 5.1, 22.2 or Wave Field Synthesis results in even more production steps, namely the spatial authoring, to accomplish a rich experience for the audience. This paper proposes a system that enables the audio engineers to work together on the same project. The proposed system is planned to be implemented for an existing spatial authoring software but can be utilized by any other application that organizes its data in a tree structured way. Three major use cases, i.e., Single User, Work Space, and Work Group, are introduced and analyzed.
Convention Paper 7743 (Purchase now)
P16-5 Spatial Sampling Artifacts of Wave Field Synthesis for the Reproduction of Virtual Point Sources—Sascha Spors, Jens Ahrens, Deutsche Telekom Laboratories, Techniche Universität Berlin - Berlin, Germany
Spatial sound reproduction systems with a large number of loudspeakers are increasingly being used. Wave field synthesis is a reproduction technique using a large number of densely placed loudspeakers (loudspeaker array). The underlying theory, however, assumes a continuous distribution of loudspeakers. Individual loudspeakers placed at discrete positions constitute a spatial sampling process that may lead to sampling artifacts. These may degrade the perceived reproduction quality and will limit the application of active control techniques like active room compensation. The sampling artifacts for the reproduction of plane waves have already been discussed in previous papers. This paper derives the spatial sampling artifacts and anti-aliasing conditions for the reproduction of virtual point sources on linear loudspeaker arrays using wave field synthesis techniques.
Convention Paper 7744 (Purchase now)