## Past News

Past news

PhD Position at the Acoustics Research Institute

The Acoustics Research Institute of the Austrian Academy of Sciences offers a PhD positition for three years funded by the FWF.

The candidate will work on the research project BIOTOP: Adaptive Wavelet and Frame Techniques for Acoustic BEM'', which is carried out in collaboration with the University of Basel and the Philipps-University of Marburg. The project and the PhD position is funded by the Austrian Science Fund (FWF), the Acoustics Research Institute is located in Vienna, Austria.

Research Topics:

• Parametric mesh generation from scanned data of the human head.

• Implementation and testing of the algorithms.

• Adaptive wavelet and frame methods for the numerical solution of integral equations on manifolds.

• Frames in acoustics.

General Qualifications:

• Diplom, Master's or equivalent degree in audio engineering, mathematics or a similar field.

• Basic knowledge of numerical mathematics, including the boundary element methods.

• Programming skills in C or C++, Matlab.

• Basic understanding of signal processing and frames.

• The candidate should be able to integrate into a multi-disciplinary research team.

As the project is a joint DACH project of research groups in Germany, Austria and Switzerland, the candidate will be required to travel and spend longer periods (about 3 months) at the partner institutes in Basel and Marburg.

The gross (pre-tax) salary is EUR 27.066,20 per year, according to the personal cost rates of the FWF, the work time is 30 hours per week. This post is available from 15 May 2013 and will be offered for 36 months.

Applicants should submit a letter of application describing their suitability for this position and interest in the project, and their curriculum vitae to

The application deadline is April 7, 2013.

The Austrian Academy of Sciences is an equal-opportunity employer, women and minorities are encouraged to apply.

Nicki Holighaus has sucesfully defended his PhD Thesis Theory and implementation of adaptive time-frequency transforms.

BIOTOP: Adaptive Wavelet and Frame techniques for acoustic BEM. Boundary Integral Operator Solution Techniques with Optimal Properties

Main Applicant: Wolfgang Kreuzer (Austrian Academy of Sciences, Acoustics Research Institute)

Co-Applicants: Peter Balazs (Austrian Academy of Sciences, Acoustics Research Institute), Stephan Dahlke (Phillipps-University Marburg) and Helmut Harbrecht (University Basel)

Start of the Project: 01. May 2013

The projects aims at developing efficient methods to calculate head related transfer functions (HRTFs). HRTFs describe the acoustic filtering effect of pinna (outer ear), head and torso on incoming sound. Thus, they are fundamental for sound localization in humans, for example the detection of an approaching car. For acoustic simulations the boundary element method (BEM) is a commonly used tool. However, the BEM has the big drawback that the computational effort and hardware requirement grows with the frequency. As HRTFs need to be calculated for frequencies up to 20.000 Hertz the BEM could only be used partially for HRTF calculations in the past. The efficient algorithms developed in BIOTOP shall help to deal with this drawback and make way for an efficient calculation of HRTFs in the human audio frequency range.

In BIOTOP the number of calculations shall be reduced by using adaptive wavelet- and frame techniques, thus making the BEM feasable for HRTF-calculations. Compared to commonly used BEM basis functions, wavelets have the advantage that a wavelet transformation provides functions that can adapt better to a given distribution of the acoustic field on the head. As a generalization of wavelets, frames allow for an even more flexible construction method and thus for a better adaption to the problem at hand.

receives an ICA Young Scientist Grant, 21st International Congress on Acoustics, Montreal, 2-7 June 2013.

The Board of the International Commission for Acoustics has approved the award of a Young Scientist Conference Attendance Grant to assist DI Ziegelwanger with the cost of participation at the forthcoming International Congress on Acoustics. DI Ziegelwanger is looking forward to attend the congress and present his paper with the Title: "Calculation of listener-specific head-related transfer functions: Effect of mesh quality". His Award will be announced in the Opening Ceremony of the Congress.

### Abstract - Calculation of listener-specific head-related transfer functions: Effect of mesh quality

The geometry of head and ears defines the listener-specific directional filtering of the incoming sound. The filtering is represented by the head-related transfer functions (HRTFs), which provide spectral features relevant for the localization of sound-sources. HRTFs can be acoustically measured or numerically calculated based on a geometric representation of the listener. While the acoustically measured HRTFs usually provide localization performance similar to that obtained in free-field listening, the performance obtained with numerically simulated HRTFs, however, heavily depends on the quality of the geometric and acoustic model of the listener used for the simulation. In this study, we show how to calculate listener-specific HRTFs with spectral features similar to that from acoustically measured HRTFs for the entire audible frequency range. We review the boundary-element method coupled with the fast-multipole method and we present details on the prerequisites like the geometry-capture technique, acoustical parameters, and the numerical algorithms. Further, the effect of the mesh quality on the HRTFs was investigated by systematically varying the average edge length from 1 to 5 mm. The HRTF amplitude spectra were analyzed and evaluated by visual comparison and in a localization model. The optimal average edge length for a fast calculation of HRTFs yielding potentially good localization performance is discussed.

### Abstract

Human sound-localization in sagittal planes (SPs) is based on spectral cues. These cues are described by head-related transfer functions (HRTFs) in terms of a linear time-invariant (LTI) system. It is assumed that humans learn to use their individual HRTFs and assign direction to an incoming sound by comparison with the internal HRTF representations. Existing SP localization models aim in simulating this comparison process to predict a listener’s response in SPs to an incoming sound. Langendijk and Bronkhorst (2002, JASA 112:1583-96) presented a probabilistic model to predict localization performance in the median SP. In this thesis this model has been extended by incorporating more physiology-related processing stages, introducing adaptation to the actual bandwidth of the incoming sound as well as to the listener’s individual sensitivity, and allowing for predictions beyond the median SP by implementing binaural weighting. Further, a stage to retrieve psychophysical performance parameters such as quadrant error rate, local polar error, or polar bias from the probabilistic model predictions has been developed and applied to predict experimental results from previous studies. The model has been also applied to evaluate and optimize a subband approximation technique for HRTFs, a computationally efficient method to render virtual auditory displays. The localization-model and subband approximation results are discussed, in particular in the light of the cost function used for the subband approximation.

http://www.dega-akustik.de/aktuelles/dega_preistraeger

The acoustics research institute will help verifying the proposed mathematical concepts’ usefulness for applications in acoustics and will cooperate on frame theory research. We aim in solving special phase retrieval problems using low-dimensional projectors and semidefinite programming. We aim at reducing the measurement time of the head-related transfer functions of human listeners, a filter function that is used for human 3D sound perception. Furthermore we will investigate how accurate the statement is, often used in speech recognition, that reconstruction from Mel-Frequency Cepstral Coefficients (MFCCs) is impossible.

Martin Ehler

Vienna Research Groups for Young Investigators Call 2012 Mathematics and ...

Diana Stoeva has finished her habilitation procedure.

The Acoustics Research Institut has concluded a cooperation agreement with the IEM Institute of Music and Acoustics.

Peter Balazs becomes Senior Member IEEE.

The City of Paris granted a research fellowship for the project "Wavelets and Frames for space-time-frequency representation of acoustic wave fields".

Principle Investigator: Wolfgang Kreuzer (ARI)
Co-Applicant: Markus Noisternig (IRCAM)