Psychoacoustics & Experimental Audiology

Millions of people use headphones everyday for listening to music, for watching movies, or when communicating with others. Nevertheless, the sounds presented via headphones are usually perceived inside the head and not at their actual natural spatial position. This limited perception is inherent and results in unrealistic listening situations.

When listening to a sound without headphones, the acoustic information of the sound source is modified by our head and our torso, an effect described by the head-related transfer functions (HRTFs). The shape of our ears contributes to that modification by filtering the sound depending on the source direction. But the ear is very listener-specific – its individuality is similar to that of a finger print, and thus HRTFs are very listener-specific. When listening to sounds via headphones, the listener-specific filtering is usually not available. One of the main reasons is the difficulty in the process of acquisition of the ear shape of a person, and thus in calculation of listener-specific HRTFs.

Thus, in softpinna, we will work on the development of new methods for a better acquisition of listener-specific ear shapes of a person. Specifically, we will investigate and improve the so-called "non-rigid registration" (NRR) algorithms, applied on 3-D ear geometries calculated from 2-D photos of a person’s ears. The improvement in the quality of the 3-D ear geometries acquisition will allow computer programs to accurately calculate the listener-specific HRTFs, thus enabling the incorporation of listener-specific HRTFs in future headphone systems providing realistic presentation of spatial sounds. The new ear-shape acquisition method will vastly reduce the technical requirements for accurate calculation of listener-specific HRTFs.

This project is done in collaboration with Dreamwaves GmbH. It is supported by the Bridge Programme of the FFG

Our EEG system (actiCHamp, Brain Products) consists of 64 active scalp electrodes, several passive electrodes to be used for electrooculography (EOG), and a StimTrak unit allowing to record audio signals along with the EEG signals. For auditory stimulus presentation, we use insert earphones (ER-2; Etymotic Research) minimizing electric noise induction and able to provide a large bandwidth. 

A semi-anechoic room (6.2m × 5.5m × 2.96m) is available for acoustic measurements. Also psychoacoustic experiments like sound-localization experiments can be performed.

The room is equipped with:

  • a 22-loudspeaker array for HRTF measurement;
  • 64-microphone array for various recording approaches (beam forming, near-field holography);
  • a virtual-environment setup for tests with subjects in a virtual visual and acoustic environment controlled with a head tracker in real time.
  • equiment for speech recordings for speaker identicication


DSCN0612 Vertical circular array of 22 loudspeakers generates acoustic signals from almost every direction. The listener is placed on a computer controlled swivel chair. DSCN0614

Virtual Acoustics: Localization Model & Numeric Simulations (LocaPhoto)

LocaPhoto consisted of three parts: geometry acquisition, HRTF calculation, and HRTF evaluation by means of localization model.


Geometry acquisition

First, we have evaluated the potential of various 3-D scanners by comparing 3-D meshes obtained for some listeners (Reichinger et al, 2013). For the general means of comparison, we have created "reference" meshes by taking silicon impressions from listeners' ears and scanning them in a high-energy computer tomography scanner. While generally capable, not all 3-D scanners were able to obtain meshes of required quality, thus, limiting their application in practical end-user situations.

Further, we were working on a procedure to generate 3-D meshes directly from 2-D photos by means of photogrammetric-reconstruction algorithms. Under selected conditions, we have obtained 3-D meshes allowing to calculate perceptually-valid HRTFs (publication under preparation).

HRTF calculation

While working on the geometry acquisition, we have developed, implemented, and evaluated a procedure to efficiently calculate HRTFs from a 3-D mesh. The software package Mesh2HRTF is based on a Blender plugin for mesh preparation, an executable application based on boundary-element methods, and Matlab tool for HRTF post-processing (Ziegelwanger et al., 2015a). The evaluation was done by comparing HRTFs calculated for reference meshes to acoustically measured HRTFs. Differences between various conditions were evaluated as model predictions and sound-localization experiments. We have shown that in the proximity of the ear canal, meshes with an average edge length of 1 mm or less are required. Also, we have shown that a small area as the virtual microphone used in the calculations yields best results (Ziegelwanger et al., 2015).

In order to further improve the calculations, we have applied a non-uniform a-priori mesh grading to HRTF calculations. This method reduces the number of elements in the mesh down to 10 000 while still yielding perceptually-valid HRTFs (Ziegelwanger et al., 2016). With that method, HRTF calculations within less than an hour are achievable.

HRTF evaluation

Given the huge amount of parameters in the numerical calculations, hundreds of calculated HRTF sets had to be tested. The evaluation of HRTF quality is a complex task because it involves many percepts like directional sound localization, sound externalization, apparent source widening, distance perception, timbre changes, and others. Generally, one would like to have HRTFs generating virtual auditory scenes as realistic as natural scenes. While a model evaluating kind of "degree of realism" was out-of-reach, we focused on a very important and well-explored aspect: directional sound localization.

For sound localization in the lateral dimension (left/right), there are not may aspects requiring HRTF individualization. The listener-specific ITD, as the interaural broadband difference between the sound's time-of-arrival, can contribute, though. Thus, we first created a 3-D model of time-of-arrival able to describe the ITD with a few parameters based on listener's HRTFs (Ziegelwanger and Majdak, 2014). 

For sound localization in sagittal planes (top/down, front/back), individualization of HRTFs is a large issue. The whole process of sagittal-plane localization is still not completely understood, but the role of the dorsal cochlear nucleus (DCN) was known already at the beginning of LocaPhoto. Thus, in LocaPhoto, we have developed a model able to predict sagittal-plane sound localization performance, based on the spectral processing found in the DCN. It was rigorously evaluated in various conditions and was found to predict listener-specific localization performance quite well (Baumgartner et al., 2014).

In LocaPhoto, this model allowed to evaluate many numerically calculated HRTFs. Also, it allowed to uncover surprising properties of human sound localization (Majdak et al., 2014). It is implemented in the Auditory Modeling Toolbox (Søndergaard and Majdak, 2013). It has been used for various evaluations (Baumgartner et al., 2013) like the positioning of loudspeakers in loudspeaker-based sound reproduction (Baumgartner and Majdak, 2015). And, it serves as a basis for a 3-D sound localization model (Altoe et al., 2014) and model addressing sensorineural hearing losses (Baumgartner et al., 2016).


Austrian Science Fund (FWF, P 24124-N13)


February 2012 - October 2016


  • Baumgartner, R., Majdak, P., Laback, B. (2016): Modeling the Effects of Sensorineural Hearing Loss on Sound Localization in the Median Plane, in: Trends in Hearing 20, 1-11.
  • Ziegelwanger, H., Kreuzer, W., Majdak, P. (2016): A priori mesh grading for the numerical calculation of the head-related transfer functions , in: Applied Acoustics 114, 99 - 110.  
  • Baumgartner, R., Majdak, P. (2015): Modeling Localization of Amplitude-Panned Virtual Sources in Sagittal Planes, in: J. Audio Eng. Soc 63, 562-569.
  • Ziegelwanger, H., Kreuzer, W., Majdak, P. (2015): Mesh2HRTF: An open-source software package for the numerical calculation of head-related transfer functions, in: Proceedings of the 22nd International Congress on Sound and Vibration (ICSV). Florence, Italy, 1-8.
  • Ziegelwanger, H., Majdak, P., Kreuzer, W. (2015): Numerical calculation of head-related transfer functions and sound localization: Microphone model and mesh discretization, in: The Journal of the Acoustical Society of America 138, 208-222.  
  • Altoè, A., Baumgartner, R., Majdak, P., Pulkki, V. (2014): Combining count-comparison and sagittal-plane localization models towards a three-dimensional representation of sound localization, in: Proceedings of the 7th Forum Acusticum. Krakow, Poland, 1-6.
  • Baumgartner, R., Majdak, P., Laback, B. (2014): Modeling Sound-Source Localization in Sagittal Planes for Human Listeners., in: The Journal of the Acoustical Society of America 136, 791-802.
  • Majdak, P., Baumgartner, R., Laback, B. (2014): Acoustic and non-acoustic factors in modeling listener-specific performance of sagittal-plane sound localization, in: Frontiers in Psychology 5, 319(1-10).
  • Baumgartner, R., Majdak, P., Laback, B. (2013): Assessment of sagittal-plane sound localization performance in spatial-audio applications, in: Blauert, J. (ed.), The Technology of Binaural Listening. Berlin-Heidelberg-New York (Springer), 93-119
  • Reichinger, A., Majdak, P., Sablatnig, R., Maierhofer, S. (2013): Evaluation of Methods for Optical 3-D Scanning of Human Pinnas, in: Proceedings of the 3D Vision Conference 2013, Third Joint 3DIM/3DPVT Conference. Seattle, WA, 390-397.
  • Søndergaard, P., Majdak, P. (2013): The Auditory Modeling Toolbox, in: Blauert, J. (ed.), The Technology of Binaural Listening. Berlin, Heidelberg, New York (Springer), 33-56

Contact for more information:

Piotr Majdak (Principle Investigator)

Michael Mihocic (HRTF measurement)

AABBA is an intellectual open group of scientists collaborating on development and applications of models of human spatial hearing

AABBA's goal is to promote exploration and development of binaural and spatial models and their applications.

AABBA members are academic scientists willing to participate in our activities. We meet annually for an open discussion and progress presentation, especially encouraging to bring in students and young scientists associated with members’ projects to our meetings. Our activities consolidate in joint publications and special sessions at international conferences. As a relevant tangible outcome, we provide validated (source) codes for published models of binaural and spatial hearing to our collection of auditory models, known as the auditory modeling toolbox (AMT).


  • Executive board: Piotr Majdak, Armin Kohlrausch, Ville Pulkki

  • Regular members:
    • Aachen: Janina Fels, ITA, RWTH Aachen
    • Bochum: Dorothea Kolossa, Ruhr-Universität Bochum
    • Cardiff: John Culling, School of Psychology, Cardiff University
    • Copenhagen: Torsten Dau & Tobias May, DTU, Lyngby
    • Dresden: Ercan Altinsoy, TU Dresden
    • Ghent: Sarah Verhulst & Alejandro Osses, Ghent University
    • Guangzhou: Bosun Xie, South China University of Technology, Guangzhou
    • Helsinki: Ville Pulkki & Nelli Salminen, Aalto University
    • Ilmenau: Alexander Raake, TU Ilmenau
    • Kosice: Norbert Kopčo, Safarik University, Košice
    • London: Lorenzo Picinali, Imperial College, London
    • Lyon: Mathieu Lavandier, Université de Lyon
    • Munich I: Werner Hemmert, TUM München
    • Munich II: Bernhard Seeber, TUM München 
    • Oldenburg I: Bernd Meyer, Carl von Ossietzky Universität Oldenburg
    • Oldenburg II: Mathias Dietz, Carl von Ossietzky Universität Oldenburg
    • Oldenburg-Eindhoven: Steven van de Par & Armin Kohlrausch, Universität Oldenburg
    • Paris: Brian Katz, Sorbonne Université
    • Patras: John Mourjopoulos, University of Patras
    • Rostock: Sascha Spors, Universität Rostock
    • Sheffield: Guy Brown, The University of Sheffield
    • Tabriz: Masoud Geravanchizadeh, University of Tabriz
    • Toulouse: Patrick Danès, Université de Toulouse
    • Troy: Jonas Braasch, Rensselaer Polytechnic Institute, Troy
    • Vienna: Bernhard Laback & Robert Baumgartner, Austrian Academy of Sciences, Wien
    • The AMT (Umbrella Project): Piotr Majdak
  • Honorary member and founder: Jens Blauert

AABBA Group 2020
AABBA group as of the 12th meeting 2020 in Vienna.


Annual meetings are held at the beginning of each year:

  • 12th meeting: 16-17 January 2020, ViennaScheduleGroup photo
  • 11th meeting: 19-20 February 2019, Vienna. ScheduleGroup photo
  • 10th meeting: 30-31 January 2018, Vienna. Schedule. Group photo
  • 9th meeting: 27-28 February 2017, Vienna. Schedule.
  • 8th meeting: 21-22 January 2016, Vienna. Schedule.
  • 7th meeting: 22-23 February 2015, Berlin.
  • 6th meeting: 17-18 February 2014, Berlin.
  • 5th meeting: 24-25 January 2013, Berlin.
  • 4th meeting: 19-20 January 2012, Berlin.
  • 3rd meeting: 13-14 January 2011, Berlin.
  • 2nd meeting: 29-30 September 2009, Bochum.
  • 1st meeting: 23-26 March 2009, Rotterdam.


  • Upcoming: Structured Session "Binaural models: development and applications" at the Forum Acusticum 2020, Lyon.
  • Special Session "Binaural models: development and applications" at the ICA 2019, Aachen.
  • Special Session "Models and reproducible research" at the Acoustics'17 (EAA/ASA) 2017, Boston.
  • Structured Session "Applied Binaural Signal Processing" at the Forum Acusticum 2014, Krakòw.
  • Structured Session "The Technology of Binaural Listening & Understanding" at the ICA 2016, Buenos Aires.

Contact person: Piotr Majdak

The loudspeaker array is mounted in a semi-anechoic room (3 x 3 m). It consists of 91 loudspeakers, arranged in a spherical order, and 2 subwoofers. This high number of loudspeakers enables many possible demonstration, for instance:

  • Present sound sources from any given directions by controlling each loudspeakers separately. One possible method is by using VBAP (Vector Base Amplitude Panning).
    Example: Ambient situation like birds tweeting around the listener, rain is dropping on a virtual roof above the listeners head, thunderstorm is slowly coming over the sky....
  • Present moving sound sources.
    Example: A fly is flying around the listener.
  • Demonstrate the listener how directional hearing can be important for everyday's life ("Cocktail Party Effect").
    Example: Some listeners are talking from the same direction. The listener is not able to understand a full sentence from any of them. Once they start moving to different positions it will be much easier to focus on one of them separately, and to understand the spoken sentence.
  • Present different types of rooms and their corresponding properties: Since the loudspeaker array studio is semi-anechoic the room does not add any reverbing effect. This allows to artificially filter the sound signal by adding the early reflections (mirror sources) and diffuse reverb (FDN) effect of any given room.
    Example: A guitar is being played without any reverberations. After half the track some room effect is added and the listener has the impression of suddenly being in small reverbing room.
  • Unusual positions: The listener can be virtually positioned in any situation by placing sound sources around the listening positions.
    Example: Enjoying a classical concert from the conductor's view. 


Psychoacoustics and Experimental Audiology

We study basic auditory perception of normal-hearing (NH) and hearing-impaired people. We especially focus on spatial hearing in normal-hearing listeners and bilateral hearing via cochlear-implants (CIs), devices which seek to restore hearing in people who were previously profoundly deaf.

In the case of bilateral implantation, left-right localization of sound sources can be achieved with already now available clinical CIs. An open issue concerns the 3-dimensional localization, especially resolving the confusion between the front and back. In normal-hearing listeners, spectral cues, described by the head related transfer functions (HRTFs) help to localize sounds in all three dimensions. The fast and reliable front-back orientation is especially important for implanted children navigating in dangerous environments like heavy-traffic roads. Utilizing acoustic measurements and numerical simulations, our research aims at transmitting spatial cues to the auditory system via implant electrodes to enable CI listeners to localize sound-sources in sagittal planes. See the project "Spectral cues in auditory localization with cochlear implants"

Interaural time differences (ITDs) are the most salient cues for determining the lateral position of a sound. ITDs are also important for speech perception in noisy conditions. In CI listeners, the ITD sensitivity is limited. We investigate the perception of ITDs in NH listeners and provide algorithms to improve the ITD sensitivity in CI listeners. See our ongoing research line "Perception of interaural time differences"

By investigating basic mechanisms involved in spatial hearing, we are seeking methods to improve the spatial experience when listening to sounds like speech, and music. Our Lab Facilities allow the measurement of subject-dependent HRTFs and the creation of virtual binaural acoustics by filtering sounds with HRTFs and presenting the signals via headphones. Our setup for sound-localization experiments includes a real-time virtual visual environment, allowing the testing of arbitrary manipulations of HRTFs combined with audio-visual interactions. The research involves methods for capturing HRTFs, efficient implementations of binaural acoustics, or development of sound-localization models.

Ongoing main projects:

  • YIRG Dynamates: Dynamic auditory predictions in human and non-human primates
  • Born2Hear: Development and Adaptation of Auditory Spatial Processing Across the Human Lifespan
  • SOFA: Spatially Oriented Format for Acoustics (2013-)


Completed main projects:

  • SpExCue: Role of Spectral Cues in Sound Externalization: Objective Measures & Modeling (2016-2019)
  • ITD PsyPhy: Bilateral Cochlear Implants: Physiology and Psychophysics (2015-2019)
  • BiPhase: Binaural Hearing and the Cochlear Phase Response (2013 - 2017)
  • POTION: Perceptual Optimization of Audio Time-Frequency Representations and Coding (2014 - 2016)
  • LocaPhoto: Virtual Acoustics: Localization Model & Numeric Simulations (2012 - 2015)
  • ITD MultiEl: Binaural-Timing Sensitivity in Multi-Electrode Stimulation (2013 - 2015)
  • HRTF Imp: Time-Frequency Implementation of HRTFs (2012 - 2014)

Check our projects list for more information.