Measuring impulse responses containing complete spatial information

Traditional impulse response measurements did capture limited spatial information. Often just omnidirectional sources and microphones are employed. In some cases it was attempted to get more spatial information employing directive transdudcers: known examples are binaural microphones, figure-of-8 microphones, and directive loudspeakers. However, these approaches are not scientifically based, and do not provide an easy way to process and visualize the spatial information. On the other side, psychoacoustics studies demonstrated that "spatial hearing" is one of the dominant factors for the acoustic quality of rooms, particularly for theatres and concert halls. Of consequence, it is necessarily to reformulate the problem entirely, describing the transfer function between a source and a receiver as a time/space filter. This requires to "sample" the impulse response not only in time, but also in space. This is possible employing spherical harmonics for describing, with a predefined accuracy, the directivity pattern of both source and receiver. It is possible to build arrays of microphones and of loudspeakers, which, by means of digital filters, can provide the required directive patterns. It can be shown how this makes it possible to extract useful information about the acoustical behavior of the room, and to make high-quality auralization.