Temporal aspects of impact sounds designed for virtual environments
11 / 2002 - 04 / 2007
It is well known that time-varying aspects of everyday sounds convey a large amount of the information used by listeners in identifying the events that occur around them. In the PhD thesis of Mark Houben (J.F. Schouten School, 2002), "The Sound of Rolling Objects / Perception of size and speed", the importance of temporal properties of sound has been established for the auditory perception of the speed of rolling balls. In actual rolling, especially when the ball is small and the speed is high, it is common that the ball looses contact with the substrate and bounces on until the speed has decreased up to a level where normal rolling takes over again. It is assumed that this bouncing behaviour contains information used by the listener to estimate the size, weight and the speed of the rolling ball, although nothing is known about what information this may be. A complicating factor is that the dynamics of this bouncing is chaotic (Bapat & Sankar, 1986). Sometimes it is very regular and almost periodic; sometimes it is random-like. The project aims at describing this bouncing behaviour for balls of various sizes, weights and speeds, and to investigate the nature of the information listeners might use in estimating the size, weight and speed of rolling balls. The project should result in an algorithm for the synthesis of contact sounds to be implemented in the Department's MuSeLab for the design of natural, realistic bouncing and rolling sounds, which contribute to the naturalness and the perceived reality of the environment. Directly related to this chaotic bouncing process is the non-linear behaviour of the impacts between ball and plate or table. The sonic consequences of hard and soft impacts (velocity) and of hard and soft impactors (material) is analysed separately in the field of musical acoustics (Chaigne & Doutaut, 1996). These impacts set the plate or table into vibration, a topic where very much research has already been carried out. These results, however, are not always directly applicable to the situation of a ball rolling over a uniformly supported plate. A careful analysis has to be made to determine which aspects need to be included to come to a natural sounding simulation of the rolling sounds.