Home : Tune Toys : Expresso 
  Expresso takes a simple musical expression (literally "X") and mutates it. In each generation, transformations are applied to components of the expression. This is a fractal technique known as an L-system. The more generations there are, the larger and more complex the expression gets (and the longer it can take to compute). The output varies wildly, from boring to fascinating. Press "Mutate" a few times till you get something that looks interesting, then click on the image to play it. See Composer's Quarry for examples of output.

Transformations:
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After 20 generations the expression "X" became this:
((transpose(shuffle(echo(transpose((((echo((step((((transpose(transpose(echo(echo(X,4,6) ,4,6) ,-5) ,4) +transpose(((((transpose(shuffle(X) ,-7) +X) +(transpose(X,-7) |transpose(shuffle(X) ,-5) ) ) +transpose(((echo(transpose(X,4) ,4,6) +transpose(transpose(((X+transpose((X+X) ,4) ) +transpose(transpose(X,-5) ,7) ) ,4) ,4) ) +transpose((step((X|X) ,12) +transpose(X,-7) ) ,7) ) ,4) ) +transpose((transpose(echo((X+X) ,4,6) ,4) |arpeggio(shuffle(X) ) ) ,7) ) ,12) ) +transpose((((transpose((X|X) ,-7) +transpose(transpose(X,4) ,7) ) |(transpose(X,-5) |((X+transpose(X,4) ) +transpose(X,7) ) ) ) +shuffle(((X+transpose(X,12) ) +(X+transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,7) ) ) ) ) ,4) ) +transpose(step(shuffle((((transpose(X,-7) +transpose(step(X,12) ,4) ) +transpose(X,7) ) |transpose(echo(X,4,6) ,-7) ) ) ,12) ,7) ) ,12) |shuffle((step(((X+transpose(transpose(X,-5) ,7) ) |X) ,12) +transpose(step(((X+transpose(step(X,12) ,7) ) +step(arpeggio(transpose(X,-5) ) ,12) ) ,12) ,7) ) ) ) ,4,6) +((transpose(arpeggio((echo(X,4,6) |arpeggio(X) ) ) ,-7) +transpose((((echo(step(transpose((X+X) ,-5) ,12) ,4,6) +transpose(step(transpose(shuffle((X|X) ) ,-5) ,12) ,4) ) +transpose(shuffle(transpose(X,-5) ) ,7) ) |(X+transpose(X,7) ) ) ,4) ) +transpose(arpeggio((transpose(transpose(shuffle(transpose(step(X,12) ,-7) ) ,-5) ,-5) +echo((arpeggio(X) +transpose(X,4) ) ,4,6) ) ) ,7) ) ) |step(transpose(((echo(((transpose(X,-5) +transpose(step(X,12) ,12) ) +transpose(transpose(transpose(X,4) ,-7) ,12) ) ,4,6) +transpose(((transpose((((X+transpose(X,4) ) +transpose(X,7) ) +transpose(transpose(transpose(X,-7) ,-5) ,12) ) ,-7) +transpose((transpose((transpose(X,-5) |((X+transpose(X,4) ) +transpose(X,7) ) ) ,-5) |X) ,7) ) |transpose(transpose((X+transpose(X,12) ) ,4) ,-5) ) ,12) ) +transpose((transpose(transpose(shuffle(transpose((transpose(X,-7) +((X+transpose(X,4) ) +transpose(X,7) ) ) ,4) ) ,4) ,-7) |transpose(((transpose(transpose(X,4) ,-7) |((X+transpose(X,7) ) +transpose((transpose(X,-5) +transpose((X|X) ,4) ) ,12) ) ) +transpose(transpose((((((X+transpose(X,12) ) +transpose((X+X) ,7) ) +transpose(transpose(transpose(X,-7) ,-7) ,4) ) +transpose(arpeggio((X+X) ) ,7) ) +transpose(echo(((X+transpose(X,4) ) +transpose(X,7) ) ,4,6) ,12) ) ,-7) ,12) ) ,-5) ) ,12) ) ,-5) ,12) ) |(((((transpose(transpose((X+X) ,-5) ,-5) +transpose(step(step(step(arpeggio((X+transpose(X,7) ) ) ,12) ,12) ,12) ,-5) ) |step(shuffle(transpose(((((transpose(X,-7) +transpose(X,4) ) +transpose(transpose(X,4) ,7) ) |transpose(echo(X,4,6) ,-7) ) |transpose(X,4) ) ,-5) ) ,12) ) +transpose(((transpose(echo(arpeggio(((step(X,12) +transpose(echo(X,4,6) ,12) ) +(transpose(X,4) +X) ) ) ,4,6) ,-5) |transpose(transpose(shuffle((((X+(X+transpose(X,7) ) ) +transpose((echo(shuffle(X) ,4,6) |(transpose(X,-5) |step(X,12) ) ) ,4) ) +transpose(arpeggio(((X+transpose(X,4) ) +transpose((X|X) ,7) ) ) ,7) ) ) ,4) ,-5) ) +transpose(step(transpose(((X|X) +transpose(X,-5) ) ,-5) ,12) ,12) ) ,7) ) +transpose(step(shuffle(arpeggio(transpose((arpeggio(((step(transpose(transpose(X,-5) ,-5) ,12) +transpose((arpeggio((X|X) ) +(X+transpose(step(X,12) ,12) ) ) ,4) ) +transpose((X+X) ,7) ) ) +(((step(transpose((X+X) ,-5) ,12) +transpose((transpose(transpose(X,-7) ,-5) +transpose(X,7) ) ,4) ) +transpose(transpose(arpeggio(((X+transpose(X,4) ) +transpose(X,7) ) ) ,-7) ,7) ) +transpose((transpose((X+transpose(X,7) ) ,4) |transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,4) ) ,12) ) ) ,-7) ) ) ,12) ,4) ) +transpose(transpose((((step(step(X,12) ,12) +transpose(step(echo(((X+transpose(X,7) ) |(X+X) ) ,4,6) ,12) ,7) ) +transpose((echo(transpose(transpose(((arpeggio((X|X) ) +transpose(X,4) ) +transpose(transpose(X,4) ,7) ) ,4) ,-7) ,4,6) |arpeggio(((transpose(X,-7) +transpose(transpose(X,4) ,-7) ) +transpose(echo(step(X,12) ,4,6) ,7) ) ) ) ,7) ) |transpose((echo(((((X+transpose(X,4) ) +transpose(arpeggio(X) ,7) ) +transpose(X,12) ) +(X|shuffle((X+X) ) ) ) ,4,6) +transpose(((step(X,12) +transpose(echo(X,4,6) ,7) ) |(echo(((((transpose(X,4) +transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,4) ) +transpose(X,7) ) +transpose(X,4) ) +transpose(transpose(X,-7) ,7) ) ,4,6) |(transpose(X,-5) |transpose((X+transpose(transpose(X,4) ,7) ) ,-5) ) ) ) ,12) ) ,4) ) ,-7) ,7) ) ) ,-7) ,4,6) ) ,-7) |echo((arpeggio((((transpose(((((X+(X+X) ) +step(((transpose(X,-7) +transpose(transpose(step(X,12) ,-7) ,4) ) +transpose(step((X+transpose(X,12) ) ,12) ,7) ) ,12) ) +transpose((((arpeggio(echo((X+X) ,4,6) ) +transpose(transpose(X,-5) ,-7) ) +transpose(transpose(arpeggio(((X+transpose(X,12) ) +(X|X) ) ) ,-5) ,4) ) +transpose(((step(X,12) |shuffle(X) ) +transpose((shuffle(X) +(((X+X) +transpose((X+X) ,4) ) +transpose(echo(X,4,6) ,7) ) ) ,12) ) ,7) ) ,4) ) +transpose(transpose((X+transpose(echo(transpose(X,4) ,4,6) ,7) ) ,-7) ,7) ) ,-5) +(arpeggio(echo(transpose(transpose(transpose((X+transpose((transpose(X,4) +transpose((X|X) ,-5) ) ,12) ) ,4) ,4) ,-5) ,4,6) ) |(transpose(echo(((shuffle(X) +transpose(((transpose((X+X) ,-7) +(shuffle(X) +transpose(transpose((X+X) ,-5) ,12) ) ) +transpose(transpose(X,-7) ,-7) ) ,4) ) +transpose(arpeggio(X) ,7) ) ,4,6) ,-5) |(((((((X+transpose(X,4) ) +transpose(X,7) ) |(transpose(X,4) |(X|X) ) ) +transpose(transpose(shuffle(X) ,-7) ,12) ) +shuffle(transpose(((transpose(X,-5) +transpose(X,4) ) +transpose(step(X,12) ,7) ) ,-7) ) ) +transpose(transpose((transpose((X|X) ,-7) +((X+transpose(X,4) ) +transpose(X,7) ) ) ,4) ,12) ) +transpose(((step((X+X) ,12) |transpose(((X+X) +(X+X) ) ,-5) ) +transpose(shuffle((step(X,12) +transpose(transpose(X,4) ,7) ) ) ,12) ) ,-5) ) ) ) ) +(transpose((transpose(transpose((X+X) ,-7) ,4) |transpose(step(((X|X) +step(X,12) ) ,12) ,4) ) ,-5) |((((transpose(transpose(transpose((X+transpose(X,7) ) ,-7) ,-7) ,4) |((echo(transpose((step(arpeggio(X) ,12) |transpose((X+transpose(X,12) ) ,4) ) ,-5) ,4,6) +transpose((((X+transpose(transpose(X,4) ,12) ) +transpose(arpeggio(X) ,4) ) +transpose(arpeggio(shuffle((X+X) ) ) ,7) ) ,4) ) +transpose(((transpose(X,-7) |transpose(X,4) ) +transpose(echo(transpose(transpose(X,-5) ,-7) ,4,6) ,7) ) ,7) ) ) |transpose((transpose(transpose(((X|X) |X) ,-7) ,4) |transpose((transpose((X+transpose((X+transpose(transpose(X,4) ,12) ) ,12) ) ,4) +transpose((((transpose(X,-7) +transpose(shuffle(X) ,12) ) +(X+transpose(X,7) ) ) +transpose(transpose(X,4) ,7) ) ,12) ) ,-5) ) ,4) ) +transpose((transpose(((((transpose(X,-7) +transpose(((X+transpose(X,7) ) |(((X+X) +transpose(X,4) ) +transpose(X,7) ) ) ,4) ) +transpose((arpeggio((transpose(X,-7) +transpose((X+transpose(X,12) ) ,12) ) ) +transpose(transpose((shuffle(X) +transpose(X,7) ) ,-5) ,12) ) ,7) ) |transpose(transpose(((X+transpose((transpose(X,-7) +(X|X) ) ,4) ) +transpose(transpose(X,4) ,7) ) ,4) ,4) ) +transpose(transpose(((transpose(X,-5) +transpose(X,4) ) +transpose(transpose(X,-7) ,7) ) ,-7) ,12) ) ,-5) +transpose(step(transpose((shuffle(X) +transpose(((X+X) +transpose(X,12) ) ,-7) ) ,-7) ,12) ,-5) ) ,4) ) +transpose(((transpose(((((X+transpose(X,4) ) +transpose(X,7) ) |transpose(((step(X,12) +transpose((X|X) ,4) ) +transpose(X,7) ) ,4) ) |((transpose((X+transpose(X,12) ) ,4) +(shuffle(X) +transpose(X,7) ) ) +transpose(transpose(((X+transpose(X,12) ) +transpose((X+X) ,12) ) ,-5) ,12) ) ) ,-7) +(shuffle(transpose(((echo(X,4,6) +transpose(transpose(X,4) ,12) ) +(X|X) ) ,4) ) +transpose((transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,-7) +transpose((X+transpose(X,12) ) ,12) ) ,12) ) ) +transpose(transpose((shuffle(shuffle(transpose(X,-5) ) ) |(transpose(transpose(X,4) ,-5) +transpose(shuffle(((X|X) +transpose(X,12) ) ) ,12) ) ) ,-5) ,7) ) ,7) ) ) ) +transpose(transpose((((((((X+transpose(X,7) ) +transpose(X,12) ) |echo(transpose(X,-5) ,4,6) ) +transpose(transpose((step(X,12) +transpose(transpose((X+transpose(X,12) ) ,-7) ,7) ) ,4) ,4) ) +transpose(transpose((X+X) ,-7) ,7) ) +transpose(transpose(transpose(((X|X) |transpose(X,-7) ) ,-5) ,-5) ,7) ) +transpose(step((X+transpose(X,7) ) ,12) ,-5) ) ,-5) ,12) ) ) +transpose(transpose((arpeggio(transpose((transpose(shuffle(transpose(X,-5) ) ,-7) +transpose(transpose(((X+step(X,12) ) +transpose((((X|X) +((X+transpose(X,4) ) +transpose(X,7) ) ) +transpose(transpose((X|X) ,-5) ,7) ) ,12) ) ,-7) ,7) ) ,-7) ) +transpose(transpose((((((X+X) +transpose(((X|X) |arpeggio(X) ) ,12) ) +transpose(arpeggio(((X|X) +transpose(X,-5) ) ) ,4) ) +transpose(transpose(arpeggio(X) ,4) ,7) ) +arpeggio(arpeggio((arpeggio(X) |arpeggio((X+transpose(X,12) ) ) ) ) ) ) ,-5) ,7) ) ,-7) ,7) ) ,4,6) ) +transpose(shuffle(transpose(shuffle(transpose(transpose(transpose((shuffle(((X|X) +X) ) +transpose((shuffle(step(X,12) ) +transpose(transpose(echo(X,4,6) ,4) ,7) ) ,12) ) ,-7) ,-5) ,4) ) ,4) ) ,-5) )
random seed used was 30151908

The algorithm for Expresso is written in KeyKit, and here's the source code.