I'm on the verge of turning my master ROM in to Nintendo to start the lotcheck process, and the final piece to fall into place has been the full soundtrack. Whereas the QA ROM had only three songs in place, the final game has a full set of ten. But by "songs," I don't mean manually-arranged pieces of music in the traditional sense. Ten linear songs wouldn't fit on a DS cartridge anyway, even if we wanted to do it that way.
Yes, we're using the largest available cartridge size, but we've squeezed something like 20 hours of unique musical moments into that space. We did this not through compression, but instead by making the music arrangement dynamic and procedurally controlled. A "song" in Diamond Trust is a folder full of loops that is fed into the music engine. The engine arranges the music in realtime based on the current state of the game.
The following video gives a demo of some of the inner workings of the music engine (which are not visible at all in the final game):
As I worked on this rather simple engine and witnessed how easily Tom could fit a wide variety of music compositions into it, I was reminded of Chris Hecker's Structure vs. Style dichotomy. In this case, the music is broken down into a well-defined, structured format that my code can easily (and blindly) handle, but it's flexible enough to permit all sorts of stylistic variation and creative control on the part of the musician.
This approach grew out of necessity: how do you make a soundtrack for a short game that people will play over and over? There are no cutscenes or set pieces to hook traditional film score moments onto. And just playing looping songs gets grating quickly. Full-on computer-generated music (like that from Inside a Star-filled Sky) can be endless without grating repetition, but the themes and presentation in Diamond Trust demanded musical styles that are impossible to generate completely procedurally. Plus, I needed a system that was compatible with Tom's well-developed music production habits (which include the recording of real musical instruments and human voices).
The resulting system can also be seen as one that wrings a huge amount of musical variety from a small base set of hand-crafted source material through sheer combinatorics. Yes, I said 20 hours of unique musical moments, but those moments are strung together into practically infinite variations of song arrangements.