Product Review: Real Sound Synthesis for Interactive Applications

Author: by Jeremy Jessup

Real Sound Synthesis for Interactive Applications describes elementary and advanced techniques to simulate the audio components of dynamic systems using physics. While the book is not specifically directed toward game developers, the application to game development is clear. The book's organization is easily to follow through three sections detailing digital audio, sound modeling, and simulation of real-world instruments.

The first section (chapters 1-3) defines digital audio, compression, wave synthesis, and simple filtering techniques. These chapters serve as the foundation for what follows, defining common asset formats and techniques currently used in games.

The second section (chapters 4-8) introduces sound modeling through simplified physical systems, such as an ideal spring, and Fourier series equations. While an understanding of college physics and calculus is helpful (especially if you'd like to code these methods), the book doesn't require it or get bogged down in theory or mathematical proofs.

The last section (chapters 7-16) provides physics equations that allow for the simulation of real-world instruments (string instruments, tubes, and multi-dimensional objects). Each chapter describes a different system based on Fourier construction, filtering, and physics-based equations. It's the heart of the book and most interesting.

The clean organizational layout made it easy for me to refer back to previous sections when I felt the need. In many cases, however, I found the writing to be a little too condensed and wished for a paragraph describing a concept rather than the sentence provided. Cook does supply references at the end of each chapter for those readers seeking additional detail.

The book also includes a CD containing audio samples of the topics discussed throughout the book. While reading the book, it was useful to be able to hear the point made or technique used in the text. The CD also contains Cook's sound synthesis toolkit and several examples of instruments highlighted in the last section.

Unfortunately, real-time sound synthesis in games currently has a limited place. Due to the complex calculations of Fourier series, fast digital signal processor chips are required to simulate the audio effects without impacting the rest of the game. Minimally, filters and other simple routines outlined in the book can be written for target hardware to accomplish specialized effects, but this is nothing radically new.

However, Cook's research in simulating audio is extremely exciting. During the calculation of an object's dynamic behavior (such as collision response, striking, falling, and moving), a minimal additional amount of time can be spent to determine the audio effects. According to Cook's findings, this amount is generally less than 5 percent of the total time required to simulate an object's physical behavior. Admittedly, these calculations are on the order of minutes versus milliseconds, but eventually Moore's law will catch up and simplifications will allow unparalleled audio effects in conjunction with physical simulation.

Developers and sound designers interested in the math and physics of creating real-time sounds should pick up this book. Those interested in a fascinating look at the mechanisms of dynamically producing sound might also want to give it a read, provided it's with the understanding that the direct applicability to games is at least few years away.