except for the percussion (which is loops) this is made of additive synthesis of the hailstorm algorithm on the numbers from 1 to 99. each number is treated as 1 Hz.

Consider the following operation on an arbitrary positive integer:

If the number is even, divide it by two.
If the number is odd, triple it and add one.
repeat

see: http://en.wikipedia.org/wiki/Collatz_conjecture