Sound Production and Modeling

23 S ound in multimedia, movies, games, virtual reality, and human–computer interfaces is a growing field that encompasses the disciplines of analog and digital signal processing, physics, speech, music, perception, and computer systems architecture. This overview of sound production and modeling techniques surveys the state of the art in sound technology. Sound has become a critical component in modern multimedia systems, especially multispeaker surround-sound entertainment systems. Many of the components and techniques in these systems are also applicable in virtual and augmented reality systems. With basic sound hardware now available for most (but not all, as in some palmtops) computer systems , and increasing processor speeds allowing direct real-time sound manipulation, enhancing multimodal computer–human interfaces by using the sonic channel is becoming commonplace. Sound in games and other graphics-intensive real-time applications is achieving higher levels of sophistication and promises to undergo even further advancements in realism and responsiveness. Sound is a wave phenomenon created by vibrations of physical objects or fluids. For any given medium, sound travels at a constant rate determined by the properties of that medium such as the density and bending/compression modulus. In stiff media (such as rigid bars and plates), the speed of sound is sometimes a function of the frequency of oscillation, with greater speed for increasing frequency. Some propagating sound waves are transverse, where the disturbance is orthogonal to the direction of propagation. This is evident in water waves, which displace the surface of the water up and down, yet travel perpendicular to the disturbance motion. Figure 1 shows a transverse wave in the wave traveling on a string. The transverse wave also occurs in many other solids such as membranes and plates. Other types of propagating sound waves are longitudinal, in which the disturbance is in the same direction as the propagation. This happens in air, as Figure 2 shows. Waves propagate in physical objects, but the vibration can sometimes appear much differently to observers. For example, if we lift up a string under tension at the center and release it, it appears to flop up and down, rather than the appearance of waves traveling down and back along the string. Similarly, if we strike a drumhead in the center, it appears to flop up and down (like the string, but in 2D). If we were to pick up a string near the end, and if we could observe the vibration in slow …