I think modulation is one of those complex problems that has been solved in multiple, interesting ways. You might also be interested in the v. analog modem standards.
Yeah, that's one of the cool things about music apps ... as with music hardware, there are dozens of ways to (for example) make n-pole filters and distinguish your sound and features from other people's.
Sound is an area that seems like it will generate new ideas and application possibilities for a long, long time. The fifteen-year flood of music software/hardware innovation shows no signs of abating....
