AES London 2011
Paper Session P14

P14 - Multichannel/Spatial, Part 2

Sunday, May 15, 09:00 — 12:30 (Room 1)

Russell Mason

P14-1 Spatial Analysis of Room Impulse Responses Captured with a 32-Capsule Microphone ArrayAngelo Farina, Alberto Amendola, Andrea Capra, Christian Varani, University of Parma - Parma, Italy
The authors developed a new measurement system, which captures 32-channel impulse responses by means of a spherical microphone array and a matrix of FIR filters, capable of proving frequency-independent directivity patterns. This allows for spatial analysis with resolution much higher than what was possible with obsolete sum-and-delay beamforming. The software developed for this application creates a false-color video of the spatial distribution of energy, changing with running time along the impulse response duration. A virtual microphone probe allows extraction of the sound coming from any specific direction. The method was successfully employed in three concert halls, providing guidance for correcting some acoustical problems (echo, focusing) and for placing sound reinforcement loudspeakers in optimal positions.
Convention Paper 8400 (Purchase now)

P14-2 Control of the Beamwidth of a Beamformer with a Fixed Array ConfigurationWan-Ho Cho, Chuo University - Tokyo, Japan; Marinus M. Boone, Delft University of Technology - Delft, The Netherlands; Jeong-Guon Ih, Korea Advanced Institute of Science and Technology (KAIST) - Daejeon, Korea; Takeshi Toi, Chuo University - Tokyo, Japan
The directional characteristic of the optimal beamformer of a transducer array depends not only on its hardware configuration but also on the stability factor. This parameter can be used to control the directivity of the array. In this paper a method, which is based on the proper selection strategy of the stability factor, is suggested to control the directional characteristics of the optimal beamformer without changing the array configuration. The selection method of the stability factor was investigated considering the trade-off relation between spatial resolution and noise amplification or array gain. The suggested method was applied to the problems of both microphone- and loudspeaker arrays to obtain a specific directivity pattern of high resolution with a constant beamwidth.
Convention Paper 8401 (Purchase now)

P14-3 Design 3-D High Order Ambisonics Encoding Matrices Using Convex OptimizationHaohai Sun, U. Peter Svensson, Norwegian University of Science and Technology - Trondheim, Norway
In this paper we propose a convex optimization method for the design of 3-D High Order Ambisonics (3-D HOA) encoding matrices using spherical microphone arrays, which offers the possibility to impose spatial stop-bands in the directivity patterns of all the spherical harmonics while keeping the transformed audio channels still compatible with the 3-D HOA reproduction sound format. Using the proposed convex optimization method, the globally optimal encoding matrices can be obtained, and the suitable trade-off among several design factors, e.g., response distortions in the obtained spherical harmonic, the dynamic range of matrix coefficients, i.e., the system robustness, and frequencies, can be analyzed and illustrated. The proposed convex optimization is formulated as a form of second-order cone programming that can be efficiently solved. Numerical results validate the proposed method. This method can be easily generalized to the 2-D HOA cases.
Convention Paper 8402 (Purchase now)

P14-4 Principles in Surround Recordings with HeightGuenther Theile, VDT - Geretsried, Germany; Helmut Wittek, Schoeps Mikrofone - Karlsruhe, Germany
New multichannel sound formats extending 5.1 with height channels are adding the third dimension to recordings. They provide a much wider range of spatial sound effects and allow more realism of spatial reproduction in terms of direct sound, early and late reflections, reverberation, and ambience sound. Using the example of two upper layer front and two upper layer surround complementary loudspeakers (5.1+4, known as “Auro 3D 9.1”) the psychoacoustic principles in the perception of elevated phantom sound sources, spatial depth, spatial impression, envelopment, ambient atmosphere, as well as directional stability within the sweet area are discussed. Concrete proposals for microphone configurations can evolve from these considerations.
Convention Paper 8403 (Purchase now)

P14-5 Efficient 3-D Sound Field ReproductionMincheol Shin, Filippo Fazi, ISVR, University of Southampton - Southhampton, UK; Jeongil Seo, Electronics Telecommunication Research Institute - Daejeon, Korea; Philip A. Nelson, ISVR, University of Southampton - Southampton, UK
A method is presented for efficient sound field reproduction with a loudspeaker array constituted by multiple sound sources that are three-dimensionally distributed. The physical reproduction of several target sound fields is investigated when the target sound fields are surrounded by multiple sound sources. A cost function to be minimized has been developed to obtain the optimal solution with reasonable energy distribution and sufficient sweet area when the distribution of loudspeakers is non-uniform. The performance of the proposed method is verified by the results of computer simulations and subjective tests in the cases of NHK 22.2 and ETRI 10.2 channel configurations.
Convention Paper 8404 (Purchase now)

P14-6 On the Scattering of Synthetic Sound FieldsJens Ahrens, Sascha Spors, Deutsche Telekom Laboratories, Technische Universität Berlin - Berlin, Germany
In sound field synthesis a given arrangement of elementary sound sources is employed in order to synthesize a sound field with given desired physical properties over an extended region. The calculation of the driving signals of these secondary sources typically assumes free-field propagation conditions. The present paper investigates the scattering of such synthetic sound fields from unavoidable scattering objects like the head and body of a person apparent in the target region. It is shown that the basic mechanisms are similar to the scattering of natural sound fields. Though, synthetic sound fields can exhibit properties different to those of natural sound fields. Consequently, in such cases also the scattered synthetic sound fields exhibit properties different to those of scattered natural sound fields.
Convention Paper 8405 (Purchase now)

P14-7 Toward Mass-Customizing Up/Down Generic 3-D Sounds for Listeners: A Pilot Experiment Concerning Inter-Subject VariabilityJohn Au, Richard So, Andrew Horner, The Hong Kong University of Science & Technology - Clearwater Bay, Kowloon, Hong Kong
The “delay-and-add” theory (Hebrank and Wright, 1974) was used to calculate 4068 matching scores between each of the 192 HRTFs and the dimensions of 12 pairs of ears for two incident sound directions (30 degrees up and 30 degrees down). Five HRTFs with 0, 25, 50, 75, and 100th percentile average matching scores were selected for two incident directions. These 10 HRTFs were used to produce 10 sound cues (5 from 30 degrees up and 5 from 30 degrees down). Ten listeners participated in a sound localization experiment to localize the 10 sound cues presented in random order and with 5 repetitions. Preliminary results indicated that matching scores can explain up to 22% of the inter-subject variations in localization errors. Potential applications are discussed.
Convention Paper 8406 (Purchase now)

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