I've gotta say, making a sound like this is one of the very obvious things to do with any synthesizer that has more than one oscillator (which is most of them) and which allows pitch modulation (again, most of them). I made it by accident some 20 years ago when I was learning to program my first analog synth and didn't know about the similarity to the THX sound until someone pointed it out to me (I grew up outside the US and had never been to an Imax presentation at that time).
