AES San Francisco 2010
Paper Session P15

Saturday, November 6, 9:00 am — 1:00 pm (Room 220)

Paper Session: P15 - Multichannel Audio Playback

Alex Voishvillo

P15-1 Why Ambisonics Does WorkEric Benjamin, Suround Research - Pacifica, CA, USA; Richard Lee, Pandit Littoral - Cookstown, Australia; Aaron Heller, SRI International - Menlo Park, CA, USA
Several techniques exist for surround sound, including Ambisonics, VBAP, WFS, and pair-wise panning. Each of the systems have strengths and weaknesses but Ambisonics has long been favored for its extensibility and for being a complete solution, including both recording and playback. But Ambisonics has not met with great critical or commercial success despite having been available in one form or another for many years. Some observers have gone so far as to suggest that Ambisonics can’t work. The present paper is intended to provide an analysis of the performance of Ambisonics according to various psychoacoustic mechanisms in spatial hearing, such as localization and envelopment.
Convention Paper 8242 (Purchase now)

P15-2 Design of Ambisonic Decoders for Irregular Arrays of Loudspeakers by Non-Linear OptimizationAaron J. Heller, SRI International - Menlo Park, CA, USA; Eric Benjamin, Surround Research - Pacifica, CA, USA; Richard Lee, Pandit Littoral - Cooktown, Queensland, Australia
In previous papers, the present authors described techniques for design, implementation, and evaluation of Ambisonic decoders for regular loudspeaker arrays. However, to accommodate domestic listening rooms, irregular arrays are often required. Because the figures of merit used to predict decoder performance are non-linear functions of loudspeaker positions, non-linear optimization techniques are needed. In this paper we discuss the implementation of an open-source application based on the NLopt non-linear optimization software library that derives decoders for arbitrary arrays of loudspeakers, as well as providing a prediction of their performance using psychoacoustic criteria, such as Gerzon’s velocity and energy localization vectors. We describe the implementation and optimization criteria and report on listening tests comparing the decoders produced.
Convention Paper 8243 (Purchase now)

P15-3 Discrete Driving Functions for Wave Field Synthesis and Higher Order AmbisonicsCésar D. Salvador, Universidad de San Martín de Porres - Lima, Peru
Practical implementations of physics-based spatial sound reproduction techniques, such as Wave Field Synthesis (WFS) and Higher Order Ambisonics (HOA), require real-time filtering, scaling, and delaying operations on the audio signal to be spatialized. These operations form the so-called loudspeaker’s driving function. This paper describes a discretization method to obtain a rational representation in the z-plane from the continuous WFS and HOA driving functions. Visual and numerical comparisons between the continuous and discrete driving functions, and between the continuous and discrete sound pressure fields, synthesized with circular loudspeaker arrays, are shown. The percentage discretization errors, in the reproducible frequency range and in the whole listening area, are in the order of 1%. A methodology for the reconstruction of immersive soundscapes composed with nature sounds is also reported as a practical application.
Convention Paper 8244 (Purchase now)

P15-4 Reducing Artifacts of Focused Sources in Wave Field SynthesisHagen Wierstorf, Matthias Geier, Sascha Spors, Technische Universität Berlin - Berlin, Germany
Wave Field Synthesis provides the possibility to synthesize virtual sound sources located between the loudspeaker array and the listener. Such sources are known as focused sources. Previous studies have shown that the reproduction of focused sources is subject to audible artifacts. The strength of those artifacts heavily depends on the size of the loudspeaker array. This paper proposes a method to reduce artifacts in the reproduction of focused sources by using only a subset of loudspeakers of the array. A listening test verifies the method and compares it to previous results.
Convention Paper 8245 (Purchase now)

P15-5 On the Anti-Aliasing Loudspeaker for Sound Field Synthesis Employing Linear and Circular Distributions of Secondary SourcesJens Ahrens, Sascha Spors, Deutsche Telekom AG Laboratories - Berlin, Germany
The theory of analytical approaches for sound field synthesis like wave field synthesis, nearfield compensated higher order Ambisonics, and the spectral division method requires continuous distributions of secondary sources. In practice, discrete loudspeakers are employed and the synthesized sound field is corrupted by a number of artifacts that are commonly referred to as spatial aliasing. This paper presents a theoretical investigation of the properties of the loudspeakers that are required in order to suppress such spatial aliasing artifacts. It is shown that the employment of such loudspeakers is not desired since the suppression of spatial aliasing comes by the cost of an essential restriction of the reproducible spatial information when practical loudspeaker spacings are assumed.
Convention Paper 8246 (Purchase now)

P15-6 The Relationship between Sound Field Reproduction and Near-Field Acoustical HolographyFilippo M. Fazi, Philip Nelson, University of Southampton - Southampton, UK
The problem of reproducing a desired sound field with an array of loudspeakers and the technique known as Near-Field Acoustical Holography share some fundamental theoretical aspects. It is shown that both problems can be formulated as an integral equation that usually defines an ill-posed problem. The example of spherical geometry and planar geometry is discussed in detail. It is shown that for both the reproduction and the acoustical holography cases, the ill-conditioning of the problem is greatly affected by the distance between the source layer and the measurement/control surface.
Convention Paper 8247 (Purchase now)

P15-7 Surround Sound with Height in Games Using Dolby Prologic IIzNicolas Tsingos, Christophe Chabanne, Charles Robinson, Dolby Laboratories - San Francisco, CA, USA; Matt McCallus, RedStorm Entertainment - Cary, NC, USA
Dolby Pro Logic IIz is a new matrix encoding/decoding system that enables the transmission of a pair of height channels within a conventional surround sound stream (e.g. 5.1). In this paper we provide guidelines for the use of Pro logic IIz for interactive gaming applications including recommended speaker placement, creation of elevation information, and details on how to embed the height channels within a 5- or 7-channel stream. Surround sound with height is already widely available in home-theater receivers. It offers increased immersion to the user and is a perfect fit for 2-D or stereoscopic 3-D video games.
Convention Paper 8248 (Purchase now)

P15-8 Optimal Location and Orientation for Midrange and High Frequency Loudspeakers in the Instrument Panel of an Automotive InteriorRoger Shively, Harman International - Novi, MI, USA; Jérôme Halley, Harman International - Karlsbad, Germany; François Malbos, Harman International - Chateau du Loir, France; Gabriel Ruiz, Harman International - Bridgend, Wales, UK
In a follow-up to a previous paper (AES Convention Paper # 8023, May 2010) using the modeling process described there for modeling loudspeakers in an automotive interior, the optimization of midrange and of high frequency tweeter loudspeakers’ positions for best acoustic performance in the driver's side (left) and passenger's side (right) of automotive instrument panel is reported on.
Convention Paper 8249 (Purchase now)

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