Size, shape, and material properties of sound models

Recent psychoacoustic studies dealt with the perception of some physical object features, such as shape, size or material. What is in many cases clear from everyday experience, that humans are sensitive to these features, has been proved experimentally in some controlled conditions, using either real-world or synthetic sounds. A 3D object can be described by its shape, size, material, position and orientation in space, color, surface texture, etc.. Leaving on a side those features that are purely visual (e.g., color), and those features that are only relevant for the "where" auditory subsystem, we are left with shape, size, and material as relevant "ecological" dimensions of sounding objects. This chapter addresses each of these three dimensions as they are representable in signal- or physics-based models. Section 6.1 uses geometry-driven signal models to investigate how size and shape attributes are conveyed to the listener. We bear in mind that ecological acoustic signals tell us a lot about how the objects interact with each other, i.e., about the excitation mechanisms. Indeed, it is the case that different kinds of excitation highlight different features of resonating objects. Even simple impact sounds can elicit the perception of two objects simultaneously, a phenomenon called "phenomenal scission" by some perceptionists (see chapter 2). Section 6.2 stresses the importance of accurate simulation of interaction mechanisms, in particular for calibrating the physical parameters in a sound model in order to render an impression of material by listening to sound sources.