The design splits the implementation into two layers. The first is generic to all platforms, written in a portable subset of C++, providing a rich and consistent interface for the game or application audio programmer to work with. It wraps an inner physical layer which tailors the output of the platform-independent logical layer to the most suitable hardware or software interface provided by the platform vendor.
Layers and threads of the audio runtime systems explained in the book
The scheme described has been implemented and shipped on a dozen platforms, for four game engines and five asset toolchains, with software and hardware mixing, on big and little-endian 32- and 64-bit processors from Intel, AMD, MIPS, ARM and PowerPCs.