Advantages of binaural room synthesis for research and fitting of hearing aids, cochlear implants, electro-acoustical stimulation, and combined systems

Binaural room synthesis is a sound reproduction technology that is, for a normal hearing listener, based on convolution of the sound signals to be reproduced with the impulse responses of the sound pressure propagation paths from the sources to be simulated to the listener’s eardrums. The convolution products are then presented by adequately equalized, appropriate headphones. The simulation of arbitrary acoustical reproduction environments is possible as long as they can be regarded as linear systems, which is the case for almost all practical scenarios. If the signal processing is implemented with real-time capability and adaptively, the impulse responses can be adjusted based on the listener’s head position and orientation, gathered by a tracking system. This allows the listener to move freely while the simulated acoustical scenario, encoded by the sound pressure signals at the eardrums, remains correct. For research and fitting purposes in the field of hearing aids or cochlear implants, binaural synthesis could save effort and time by providing arbitrary acoustical environments in the laboratory. Since conventional binaural synthesis is based on the reproduction of an original scene’s sound pressure signals in front of the listener’s eardrums, it is not directly applicable to listeners using hearing aids or cochlear implants, especially when the sound pressure at the eardrums is not present or not involved in the hearing process. If cochlear implants are used in connection with hearing aids or the remaining normal hearing system, as for example with electro-acoustical stimulation, the situation becomes even more complicated. Within this contribution, the conventional theory of binaural room synthesis is adapted to the typical applications with hearing impaired listeners. Further, possible application scenarios and advantages compared to traditional methods for research and fitting in the context of hearing aids and cochlear implants are discussed.