“I hired PJ to produce music and sound effects for the “Subversion” game prototype, and the work he turned in was astonishingly well crafted. We worked together for several months on the project, during which time PJ developed a tense main theme in keeping with the high-tech-stealth nature of the game.
This was no ordinary game audio project though – each element of the track was played independently within the game engine, with its volumes linked to game properties such as suspicion, danger, curiosity.  As the game progressed different elements of the music would fade up and take over, creating an audio environment that was always unique, and crucially gave the player subtle clues as to the state of the world and its inhabitants. As security guards became suspicious of your behaviour the music would shift to match that change, and the player would know instantly something was wrong. “

– Chris Delay: Founder and Director of Introversion.

You can read the development blog entry for the system here and see what other people think!