I don't know of anything good in english on the internet, I am sure there is some, I just kind of learn this stuff at rehearsal in the group I am in. There is also this book [1] if you are really curious (its a beast of a book).

But to briefly explain what I am thinking, there is the notion of irama [2], where initially (in irama I) most instruments play something close to what is written. At some point (depending on the piece and style, but usually signaled by the drummer in Javanese gamelan) there is a transition to irama II, which sounds like everyone slowing down at first, but as soon as you get to some terminal point of the transition, certain instruments, based on their own rules, begin to "fill in" the space created by the transition. For example, if you are playing the peking, it might look like this:

main melody/irama I/balungan: 2 1 2 6

peking in irama I: 22 11 22 66

peking in irama II: 22 11 22 11 22 66 22 66

and so on

I am far from expert and so much of this is all totally different depending on region and such. But this core idea of irama and rules-based elaboration from a specific seed is somewhat always present.

Either way, just really some of the most beautiful music you will hear, highly recommend to everyone [3].

1. https://www.amazon.com/Gamelan-Manual-players-central-Javane...

2. https://en.wikipedia.org/wiki/Irama

3. https://youtu.be/3efH3WgTQRU

Interesting, thanks; though I don't think that what you describe is comparable to L-systems. Just had a look into the book "Unplayed Melodies, Javanese Gamelan and the Genesis of Music Theory" by Perlman, which I have at hand, and didn't find any indications of generative grammars or rewriting; it's rather a set of established patterns ("balungan"); this also corresponds to what my friend has learned about the traditional music in Bali (here is a recording we did together; he plays the traditional slonding instruments): http://rochus-keller.ch/?p=251. The problem with the application of fractal algorithms to music is, that music is actually not "self-similar" in the fractal sense, but there are just repetitions or variations. Music in general is not based on an ever-evolving stream of "fractal noise".

I agree that Gamelan is very beautiful music. Important western composers such as Steve Reich were there and studied the music to adopt the concepts in their compositions (see e.g. https://www.youtube.com/watch?v=TN_YSS06ZcQ&pp=ygUabXVzaWMgZ...). Here a part of the performance where you can see that Reich even adopded the orchestral layout similar to a gamelan ensemble: https://youtu.be/71A_sm71_BI?t=806.