Mini-curso e seminário sobre auralização e spherical harmonics na UFRJ


O Programa de Eng. Mecânica da COPPE/UFRJ anuncia a visita do Prof Michael Vorlander do Instituto de Acústica da RWTH Aachen University para dar um mini-curso (4 aulas) – nos dias 11 e 12 de
dezembro, sobre “Auralization and Acoustic Virtual Reality” – e um seminario – no dia 13, sobre “Spherical Harmonics and their application in Virtual Acoustics”. Horário e sala serão divulgados em breve. Outros detalhes do curso e seminario, bem como dados do palestrante, seguem abaixo. Essas atividades sao abertas, aqueles
que tenham a intenção de comparecer devem entrar em contato com o Prof. Ricardo Musafir da COPPE UFRJ através do email rem[at]mecanica.ufrj.br

Short Course on Auralization and Acoustic Virtual Reality (11 e 12 de dezembro)

INTRODUCTION
Acoustic simulation and auralization are established techniques in research, development and consulting in many fields of acoustics and noise control, such as room acoustics, sound insulation, vehicle acoustics, environmental noise and machinery noise, just to list some examples. Auralization is based on modeling the components of sound generation, transmission and radiation on the one hand, and on signal processing and spatial audio technology on the other. When it comes to real-time auralization, the acoustic stimuli can be implemented in audio-visual virtual reality systems. Virtual environments that include acoustic stimuli open the possibility of creating multimodal audio-visual demonstrations in education, investigating aspects of sound design and sound quality, and studying the influence of construction parameters on the overall listener impression. In this course, the creation of Virtual Acoustic Environments is illustrated by specific examples from
room acoustics.

OBJECTIVE

To introduce the essential physical principles, basic signal processing techniques, and system design concepts needed to have a correct understanding of how Acoustic Virtual Reality (AVR) systems operate. We will also outline application areas where AVR solutions would be appropriate and which specification and system complexity shall be considered to ensure a reasonable solution in the balance between computational effort and audio quality.

PROGRAM

1. Introduction
2. The concept of auralization
3. Fundamentals of signal processing
4. Convolution and sound synthesis
5. Characterization of sound sources
6. Sound fields in cavities and in rooms
7. Simulation of sound in rooms
8. Stochastic ray tracing
9. Image source model
10. Hybrid image source models (deterministic Ray Tracing)
11. Real-time processing
12. 3D sound reproduction and virtual reality systems

SEMINARIO (13 de dezembro, previsto paras as 10:30)

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.

MICHAEL VORLANDER
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.

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