May 6 - Special session n. 1
Microphones, array topology, and array processing
(chaired by Gary Elko)

1) Jens Meyer and Gary W. Elko
"Handling Spatial Aliasing in Spherical Array Applications."
2) Boaz Rafaely
"Spatial Sampling and Beamforming for Spherical Microphone Arrays."
3) Jerome Daniel and Nicolas Epain
"Pushing the Frequency Limits of Spherical Microphone Arrays."
4) Ramani Duraiswami, Nail A. Gumerov and Adam O'Donovan
"Spherical Arrays Near Boundaries."
5) Akihiko Sugiyama, Thanh Phong Hua, Regine Le Bouquin Jeannes, Gerard FAaucon
"A Comparative Study of Adaptation-Mode Control for Generalized Sidelobe Cancellers in Human-Robot Communication."


Special session n. 1 - abstracts


Jens Meyer and Gary W. Elko "Handling Spatial Aliasing in Spherical Array Applications."
Spherical microphone arrays are an attractive solution for many audio applications where flexible beamforming in all directions is desired. However, as with all discretely sampled array systems, spatial aliasing puts a constraint on the upper operating frequency range and therefore limits some potential applications. Simply increasing the number of sensors to overcome the effect of spatial aliasing is effective but can be expensive, especially if very high quality microphones elements are used. This paper reviews the origin of spatial aliasing for spherical arrays based on modal beamforming and investigates alternative approaches to mitigate the spatial aliasing problem. The alternative approaches are based on: spatial anti-aliasing filters, exploiting the natural diffraction of the spherical baffle and compromising the directivity at higher frequencies. All approaches are practical and can be implemented without increasing the system cost significantly.

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Boaz Rafaely "Spatial Sampling and Beamforming for Spherical Microphone Arrays."
Spherical microphone arrays have been recently studied for spatial sound recording, speech communication, and sound field analysis for room acoustics and noise control. Complementary theoretical studies presented progress in spatial sampling and beamforming methods. This paper reviews recent results in spatial sampling that facilitate a wide range of spherical array configurations, from a single rigid sphere to free positioning of microphones. The paper then presents an overview of beamforming methods recently presented for spherical arrays, from the widely used delay-and-sum and Dolph-Chebyshev, to the more advanced optimal methods, typically performed in the spherical harmonics domain.

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Jerome Daniel and Nicolas Epain "Pushing the Frequency Limits of Spherical Microphone Arrays."
Spherical microphone arrays are a useful tool for numerous applications, such as spatial audio capture and beamforming. However, these sensor arrays are known to have a limited frequency range, due to poor directivity at low frequencies and spatial aliasing at high frequencies. In this paper, we study two methods aiming at enhancing the frequency range of spherical microphone arrays without using more sensors. First, the benefit of locating the sensors at the end of cavities within the sphere is assessed through measurements and simulations. Second, we study the influence of using large membrane microphones. Finally, results show that the frequency range could be increased in both cases studied.

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Ramani Duraiswami, Nail A. Gumerov and Adam O'Donovan "Spherical Arrays Near Boundaries."
Solid spherical microphone arrays are beginning to be used for purposes such as beamforming, sound field capture and as audio cameras. They rely on the scattering of sound off their surface to achieve their purpose. This behavior is significantly affected in the presence of boundaries (floors, walls, ceilings), and the edges and corners they form. Algorithms designed for array analysis in a free field will work erroneously in this situation. We describe adaptation of the spherical microphone analysis algorithms to constructively use the scattering off the boundaries to significantly improve array performance. We also assess the influence of walls on beamforming algorithms for regular spherical arrays. Both synthetic and experimental results are presented.

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Akihiko Sugiyama, Thanh Phong Hua, Regine Le Bouquin Jeannes, Gerard FAaucon "A Comparative Study of Adaptation-Mode Control for Generalized Sidelobe Cancellers in Human-Robot Communication."
This paper presents a comparative study of adaptation-mode control (AMC) for generalized sidelobe cancellers in human-robot communication. Performance of recently proposed two AMC structures, namely, NBM-SLBM (nested blocking matrix-symmetric leaky blocking matrix) and M-SLBM (multiple symmetric leaky blocking matrix), are evaluated by computer simulations and in a real environment. In the computer simulations, it is shown that M-SLBM exhibits superior performance to NBM-SLBM. However, in the real environment, the performance of M-SLBM is degraded. This degradation comes from unexpected tonal interference in a frequency range covered by an SLBM, leading to errors. An appropriate selection between NBM-SLBM and M-SLBM is necessary based on the environment.

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