Título: Spherical Harmonics and their application in Virtual Acoustics

Prof. Michael Vorländer
RWTH Aachen University in Germany

DATA:  13/12/2012
LOCAL:  Centro de Tecnologia, Sala G-219
HORÁRIO:  10:30h
CONTATO:  This email address is being protected from spambots. You need JavaScript enabled to view it.

ABSTRACT:

Spherical Harmonics and their application in Virtual Acoustics Spherical Harmonics (SH) are a mathematical base for decomposition of physical field data in spherical coordinates. This way, discrete directional data are expressed by complex-valued weighted sums of monopoles, dipoles, quadrupoles, etc. Applications of SH in audio engineering became more and more important, especially in the area of sound recording and sound reproduction with loudspeakers. In research, new approaches for recording of musical instruments were presented, and new descriptors for spatial sound fields defined which allow an interpretation of not only temporal and spectral features but also spatial attributes.

In particular, multi-channel spherical loudspeakers became popular for control of directional radiation. They have been introduced in shapes of cubes, dodecahedra, or higher-order discrete representations of spheres. In this seminar a spherical source with a partial Gaussian distribution of 28 channels is presented. With sequential measurements and rotation of the sphere a radiation of effectively 23rd order of spherical harmonics is obtained, as long as the acoustic conditions are time-invariant. In auralization, this source can reproduce musical instruments, for example, or it can radiate directional Dirac functions (sound pointer) for detection and analysis of room reflections. Filter design and various applications are discussed as well as an approach for measurement of binaural room impulse responses reciprocally. In the latter example, the spherical loudspeaker acts as an HRTF radiator. For all applications in auralization, rotations of the source and the listener such as head orientation movements can be taken into account by multi-channel real-time convolution and dynamic filters. The theoretical background, the mechanical solution and the software components are discussed and evaluated with regard to challenges, performance, and limitations.

 

Biographical information: Michael Vorländer is a professor at RWTH Aachen University in Germany, where he has been the director of the Institute of Technical Acoustics since 1996. He finished his habilitation at Technical University Dresden in 1995 with a thesis on reciprocity calibration of microphones. He has served as Editor-in-Chief of the international journal ACTA ACUSTICA united with ACUSTICA, and was President of the European Acoustics Association in the term 2004 – 2006. Currently, he is President of the International Commission for Acoustics. Among other awards, he received the RWB Stephens Medal from the UK's Institute of Acoustics in 2005, Fellowship in the ASA in 2006, and the Caracola Award of the Spanish Acoustical Society in 2009. His main research focus is on auralization and acoustic virtual reality in its various applications in room and building acoustics, automotive, and environmental noise.