Audibility of Changes in Source Directivity for Room Acoustic Auralizations Brent Kirkwood Duration: 2 Months Full Time Equivalent (September 2002 - January 2003) Supervisor: Torben Poulsen Download Full Report (PDF) (700 KB)

Abstract Modern room acoustic software, such as ODEON Room Acoustics Software (ODEON), makes possible binaural simulations of the sound perceived by a listener in a modeled concert hall, given single or multiple models of sound sources placed in that hall. These acoustic simulations, called auralizations, provide a means of making a subjective evaluation of the sound field in the hall. Classical directivity patterns used for representing a musical instrument in such a modeled hall contain data concerning the directivity of the instrument over a full range of frequencies. This typical representation does not include variations in directivity at a particular frequency, which occur between particular tones. Instead, the pattern used represents an average of all of the instrument's tonal performance range (Otondo, Rindel, et al.). More precisely representing the directivity of a musical instrument should include the information about how the directivity changes, for a given frequency band, for various tones. This method, however, complicates the implementation and processing requirements required for simulation, and therefore should be examined prior to acceptance. The influence of using tone-specific directivity patterns has been studied by Otondo, Rindel, et al., but it is primarily the simulated objective parameters, output by ODEON, that have been compared in analyses. From these parameters, it can be observed that using a tone's specific directivity pattern instead of the average directivity pattern for an instrument can have a large impact on the calculated parameters in the simulation. Ultimately of course, it is human judgment, and not a set of parameters, that decides the quality of the "acoustics" of a room (Blauert, p. xii). From the parametric observations, it was suspected that audible differences would also exist in the auralizations, but this had not been proven in previous studies. Initial informal listening tests of similarly modeled rooms as the one described in this report proved unfruitful (Otondo Conversations). The aim of this pilot study was to make a more formal investigation of the auralizations that can be created based on average and tone-specific directivity patterns of musical instruments. It was desired to determine whether or not the differences in the directivity patterns, which lead to objective differences seen in the numerically calculated parameters, were also audible to a listener in auralizations. Results of the listening tests described in this report have indicated that audibility differences do exist between the auralizations created from average and tone-specific directivity patterns of musical instruments. Initial observations show that correlation between parametric results calculated by ODEON and the results of the listening test are also possible. Further research is required to determine if the differences heard are common to most musical instruments and tones from those instruments, or if the results are simply due to the instruments and directivity patterns chosen for testing in this project. However, initial results appear to indicate a benefit, in the form of increased authenticity of the auralization, from implementing tone-specific directivity patterns. The results from these instruments and directivities tested appear to show that information about the directivity of a particular tone has been lost when an average directivity is used in its place, and that the experience of a listener has changed because of this. Related Publications Kirkwood, B. (2003) Audibility of Changes in Source Directivity for Room Acoustic Auralizations. Internal Report Otondo, F. and Kirkwood, B. (2003) Perceived influence of changes in musical instrument directivity representation. In Proceedings of Stockholm Music Acoustics Conference (SMAC), Stockholm, Sweden, pp. 655-658. Otondo, F., Rindel, J. H., The influence of the directivity of musical instruments in a room, Acta Acustica united with Acustica, vol 90(5), pp 1178-1184, 2004. (PDF) Related Links ODEON - Room Acoustics Modeling Software. DOREMI - Directionally Optimised Representation of Musical Instruments project.