Physical Modelling for Sound Synthesis

Physical Modelling for Sound Synthesis

Eoin Mullan
DOI: 10.4018/978-1-61692-828-5.ch016
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While the first computer games synthesised all their sound effects, a desire for realism led to the widespread use of sample playback when technology matured enough to allow it. However, current research points to many advantages of procedural audio which is generated at run time from information on sound producing events using various synthesis techniques. A specific type of synthesis known as physical modelling has emerged, primarily from research into musical instruments, and this has provided audio synthesis with an intuitive link to a system’s virtual physical parameters. Various physical modelling techniques have been developed, each offering particular advantages, and some of these have been used to synthesise audio in interactive virtual environments. Refinements of these techniques have improved their efficiency by exploiting human audio perception. They have been implemented in large virtual environments and linked to third party physics engines, unveiling the potential for more realistic audio, reduced production costs, faster prototyping, and new gaming possibilities.
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Current research is realising the potential of procedural audio for generating sound effects in computer games. Procedural audio is generated from information on specific sound producing events and the result is a unique soundtrack each time a virtual environment is explored. This sound generation process often involves the physical modelling of sound producing objects from an acoustic perspective. This chapter looks back at the relevant history of physical modelling and forward to how it is set to be a part of the future of computer game audio. It is laid out in four sections. The remainder of this section gives a brief history of sound effects in computer games before discussing the shortcomings of sample playback and the potential of procedural audio and physical modelling. The second section takes a look at the evolution of physical modelling including many lessons which are to be learned from the physical modelling of musical instruments. Some specific techniques are discussed with extra emphasis placed on two techniques, modal synthesis and digital waveguide synthesis, which are particularly useful in real-time applications. The third section presents, in chronological order, the projects that have made advances in the area of physical modelling for sound synthesis in computer games and virtual environments and the last section looks at directions which future research may take as well as an industry perspective on the technique.

The earliest computer games to include sound effects synthesised them using whatever hardware was available at the time. The sounds produced were very much influenced by the limitations of the hardware. Although by today’s standards they could not be considered realistic, they were marketed as such and a “drive towards realism […] is a trend we shall see throughout the history of game sound” (Collins, 2008, p. 9). “By 1980, arcade manufacturers included dedicated sound chips known as programmable sound generators, or PSGs into their circuit boards” (Collins, 2008, p. 12). Early consoles also had sound chips that developers used to synthesise sound and again the hardware limitations influenced their work. However, as computers became more powerful, developers began to utilise recorded samples in their quest for realism. Andy Farnell, author of Designing Sound (2008), explains, “[e]arly consoles and personal computers had synthesiser chips that produced sound effects and music in real-time, but once sample technology matured it quickly took over because of its perceived realism thus synthesised sound was relegated to the scrapheap” (p. 298). Karen Collins gives a comprehensive account of the earliest chips that performed synthesis up to the first systems that were capable of playing CD-quality samples.

When sound effects are required in a virtual environment today, sample playback is the most common method of producing them (McCuskey, 2003) and it is widely used for good reason. Raghuvanshi, Lauterbach, Chandak, Manocha, and Lin (2007) state that the method of sample playback is “simple and fast”, meaning it is computationally inexpensive and straight forward to implement (p. 68). The method takes advantage of known sound design techniques that have been refined through a long history of use in the movie industry. In the introduction to Real Sound Synthesis for Interactive Applications, Perry Cook (2002) concedes that, with much effort having gone into improving the sample-based approach, “the state of the art has indeed advanced to the point of absolute realism, at least for single sounds triggered only once” (p. xi). However, there are many drawbacks with sample playback and, in an interactive environment, it cannot provide “absolute realism”.

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