INTERNATIONAL CONGRESS ON ACOUSTICS MADRID , 2-7 SEPTEMBER 2007 ROUND ROBIN COMPARISON OF HRTF MEASUREMENT SYSTEMS : PRELIMINARY RESULTS

The Head-Related Transfer Function (HRTF) can be considered as the foundation for our physical understanding of spatial hearing and the creation of spatial auditory displays through binaural technology. While previous works have considered inter-individual variations, few studies have considered the variations due to the measurement system. Due to the size and complexity of HRTF measurement systems, it is difficult for a single researcher to compare different systems, especially with the same subject. This work presents preliminary results of an on-going international round-robin study, “Club Fritz,” in which the HRTF of a unique dummy head is measured at different laboratories. Measurement systems consist of physical systems and future contributions are planned to include numerical simulations based on acquired geometrical models of the artificial head (i.e. boundary element method modeling). Various comparisons between the data sets are made. An overview of the various measurement systems, highlighting their differences is presented. Correlation and spectral analysis at common measurement points are shown, as well as a comparison of the inter-aural time difference (ITD) estimation. INTRODUCTION Over the last several decades, there have been an increasing number of studies concerning measured HRTFs [1-7]. These studies have focused a great deal of attention on inter-positional differences (localization cues) and the inter-individual differences between measured HRTFs. In reviewing the literature, it is readily apparent that no two HRTF measurement systems are identical or even similar in terms of architecture, software, etc. It is therefore interesting and in some cases even symptomatic to compare both the physical differences between measurement systems and the magnitude of differences in measured HRTFs from a single test specimen. To this aim, the authors initiated a measurement campaign project whereby the HRTFs of a single and unique dummy head would be measured by various institutions. A Neumann KU-100 dummy head (sometimes referred to as “Fritz II” to distinguish it from its predecessors, the KU80 and KU-81) was chosen due to its ease of transport and shipping (see Figure 1). Such was the beginning of “Club Fritz”, which is considered to be an ongoing study. With each year, it is hoped that more institutions will join the campaign. The procedural principles of “Club Fritz” are simple. A participating institution, upon receipt of Fritz, performs an HRTF measurement following their standard procedure. Required measurements include raw Head-Related Impulse Responses (HRIRs) using the dummy head’s internal microphones. Additional measurements, using other microphones, are recommended, along with free-field compensated data. Data may also be re-submitted. A standard simple Matlab structure format has been adopted to facilitate homogeneity of analysis. Data is available to other participants for research purposes, but is not as yet freely available to the public. All published analyses must maintain anonymity of the source data institution. Any institution wishing to join this measurement campaign should contact the authors.