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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Phrase for X:
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After 20 generations the expression "X" became this:
(transpose((arpeggio(arpeggio(transpose(((transpose(((((transpose((X+transpose(X,7) ) ,4) +transpose(transpose((X|X) ,-7) ,4) ) +transpose((transpose(X,-5) +transpose(transpose(X,4) ,7) ) ,7) ) +transpose(((transpose(arpeggio(transpose(X,-7) ) ,4) +transpose(shuffle(X) ,4) ) +transpose(X,7) ) ,12) ) +(transpose(transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,4) ,-7) +transpose(step(X,12) ,7) ) ) ,4) +shuffle(((transpose(transpose(X,-5) ,-7) +transpose((transpose(((X+X) |X) ,-7) +transpose((X+transpose(transpose(X,-7) ,7) ) ,12) ) ,4) ) +transpose(transpose(transpose(X,-7) ,-7) ,7) ) ) ) +transpose(shuffle(step(transpose(echo(X,4,6) ,4) ,12) ) ,12) ) ,-7) ) ) +((((transpose((((((arpeggio(X) +transpose(echo(X,4,6) ,7) ) +step(((X+transpose(X,12) ) |(X+transpose(X,12) ) ) ,12) ) |(transpose(step(transpose((X+X) ,-5) ,12) ,4) +transpose(((((X+transpose(transpose(X,-5) ,4) ) +transpose(shuffle(X) ,7) ) +transpose((X|X) ,4) ) +transpose(transpose(step((X+X) ,12) ,-7) ,7) ) ,12) ) ) +(transpose((transpose(X,-5) +transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,7) ) ,-5) |shuffle(transpose((X+transpose(X,12) ) ,4) ) ) ) +transpose(transpose(echo((transpose(transpose(transpose(X,-7) ,-7) ,4) |transpose((echo(X,4,6) +transpose((transpose(X,4) +echo(X,4,6) ) ,12) ) ,-5) ) ,4,6) ,-7) ,7) ) ,-5) +transpose(arpeggio(((transpose(arpeggio(((X+transpose((X+transpose(X,12) ) ,12) ) +transpose(((X+X) +X) ,7) ) ) ,4) +transpose((((step(X,12) |transpose(X,-5) ) +transpose(echo(X,4,6) ,4) ) +transpose((X+transpose(X,7) ) ,7) ) ,7) ) +transpose(echo(((transpose(transpose(shuffle(transpose(echo((((X|X) |transpose(X,-7) ) +(X|X) ) ,4,6) ,-5) ) ,4) ,-5) +transpose(((step(X,12) +transpose((((X+X) +shuffle(X) ) +transpose(((X|X) +transpose(X,12) ) ,7) ) ,4) ) +transpose(echo(step((X|transpose(X,4) ) ,12) ,4,6) ,7) ) ,4) ) +transpose(((((arpeggio((X+transpose(X,12) ) ) |(shuffle(X) +transpose(arpeggio(transpose(X,4) ) ,7) ) ) +transpose(transpose((X+transpose(echo(X,4,6) ,7) ) ,-5) ,4) ) +transpose(transpose((X+transpose(transpose(X,-5) ,12) ) ,4) ,7) ) +transpose((echo(X,4,6) |shuffle(((X+transpose(X,12) ) +transpose((X+transpose(X,12) ) ,7) ) ) ) ,12) ) ,7) ) ,4,6) ,12) ) ) ,4) ) +transpose((((((transpose((X|X) ,-5) |transpose(transpose(X,-5) ,-5) ) |((echo(transpose(X,-7) ,4,6) +arpeggio((X|(transpose(X,-7) +(X+transpose(X,12) ) ) ) ) ) +transpose((X+transpose(echo(shuffle((X+X) ) ,4,6) ,7) ) ,4) ) ) +transpose(((transpose(X,-7) +transpose(transpose(((echo(X,4,6) +transpose((X+transpose(X,12) ) ,4) ) +transpose((transpose(X,-7) +((X|X) |(X+transpose(X,12) ) ) ) ,7) ) ,-7) ,4) ) +transpose(transpose(arpeggio(transpose(X,4) ) ,-7) ,12) ) ,7) ) +transpose((echo(transpose((echo((shuffle(X) +X) ,4,6) |transpose(((X+X) +transpose(((X|X) |X) ,7) ) ,4) ) ,4) ,4,6) +transpose(transpose((transpose(echo(X,4,6) ,4) +transpose(transpose(echo(echo(X,4,6) ,4,6) ,4) ,12) ) ,-5) ,12) ) ,4) ) +transpose(transpose(step(transpose(transpose((((((X+step(X,12) ) +transpose(transpose(X,-7) ,12) ) +transpose(transpose((X|transpose(X,4) ) ,-5) ,4) ) +transpose(transpose(echo(transpose(X,-7) ,4,6) ,4) ,7) ) |transpose((((X+transpose(X,7) ) +transpose(X,12) ) +transpose(X,12) ) ,4) ) ,-5) ,-7) ,12) ,4) ,-5) ) ,7) ) +(arpeggio((echo(step(((step(X,12) |(((X+transpose(X,4) ) +transpose(X,7) ) +transpose(transpose(X,-5) ,7) ) ) +transpose(transpose((X|(X+X) ) ,4) ,7) ) ,12) ,4,6) |transpose(transpose(transpose(transpose(X,-7) ,4) ,4) ,-7) ) ) +(transpose((transpose((echo((transpose(transpose(X,-7) ,-7) +transpose(transpose(echo(X,4,6) ,-7) ,-7) ) ,4,6) |transpose(echo((((transpose(X,-7) +transpose((transpose(X,-5) +transpose(transpose(X,-5) ,12) ) ,4) ) +transpose((transpose(X,4) +X) ,7) ) +transpose((transpose(transpose(X,4) ,-7) |X) ,12) ) ,4,6) ,4) ) ,4) |transpose(transpose(transpose(transpose(transpose(transpose(X,-5) ,-7) ,-5) ,-7) ,-7) ,4) ) ,-5) |arpeggio((((transpose(((transpose((X+transpose(X,7) ) ,-5) +transpose(echo(X,4,6) ,4) ) +transpose(((X+transpose(X,7) ) +X) ,7) ) ,4) +transpose(transpose((arpeggio((X|X) ) +transpose((X+transpose(X,12) ) ,7) ) ,-5) ,4) ) +transpose((transpose((shuffle(shuffle(X) ) +transpose(transpose((X+X) ,-5) ,12) ) ,-5) +transpose(shuffle((transpose(arpeggio(transpose(X,-5) ) ,4) +transpose((((((transpose(X,4) +transpose((X+X) ,4) ) +transpose(X,7) ) +transpose(arpeggio(X) ,-5) ) +echo(transpose(X,-5) ,4,6) ) +transpose((transpose(transpose(X,4) ,4) +transpose(transpose(step((X+transpose(X,7) ) ,12) ,-7) ,7) ) ,12) ) ,12) ) ) ,7) ) ,7) ) +transpose((arpeggio(transpose(transpose((transpose(X,4) +step(X,12) ) ,-7) ,-7) ) |((((X+X) +arpeggio((X+transpose(X,7) ) ) ) +transpose(echo(transpose(transpose((X+transpose(X,12) ) ,-7) ,-7) ,4,6) ,7) ) |transpose(transpose(X,-5) ,-7) ) ) ,-5) ) ) ) ) ) +transpose(transpose(step((transpose(shuffle(((((transpose(X,-5) +transpose((((X+transpose(X,4) ) +transpose(X,7) ) |X) ,7) ) +transpose(echo(step(X,12) ,4,6) ,7) ) +transpose((shuffle((((X+transpose(X,12) ) +transpose(transpose(X,4) ,4) ) +transpose(X,7) ) ) +transpose(((X+transpose(X,12) ) +(X+echo(X,4,6) ) ) ,12) ) ,12) ) |step((X+transpose((echo(((step(X,12) +transpose(transpose(X,-5) ,4) ) +transpose(X,7) ) ,4,6) |echo(X,4,6) ) ,7) ) ,12) ) ) ,-7) +(transpose((shuffle(shuffle(transpose(transpose(X,-5) ,4) ) ) +transpose(transpose(transpose(X,4) ,-7) ,-5) ) ,4) +transpose(arpeggio(arpeggio((X|transpose((X|X) ,4) ) ) ) ,7) ) ) ,12) ,4) ,-7) ) ) ,-7) |((transpose((step((transpose((((transpose(X,-5) +((X+transpose(X,4) ) +transpose(X,7) ) ) +transpose(transpose(X,-7) ,12) ) +transpose(shuffle(X) ,12) ) ,-5) +(((transpose(((X+transpose(X,7) ) +transpose(X,4) ) ,-5) +transpose(((((X+X) +transpose(transpose(X,-7) ,12) ) +(arpeggio(X) +transpose((X|X) ,7) ) ) |transpose(arpeggio(echo(step(X,12) ,4,6) ) ,4) ) ,7) ) +transpose(transpose(transpose(echo(transpose((X+transpose(X,7) ) ,-7) ,4,6) ,-7) ,-5) ,4) ) +transpose((transpose(shuffle((X+transpose(X,-5) ) ) ,-5) +transpose(echo((transpose(transpose(X,-7) ,-5) +transpose(transpose(X,4) ,7) ) ,4,6) ,-7) ) ,7) ) ) ,12) |((shuffle(((arpeggio((((X+transpose(X,7) ) |X) |(X+X) ) ) +transpose((arpeggio(((X|X) |X) ) +transpose(transpose(transpose(transpose((X+transpose(X,7) ) ,-5) ,4) ,-5) ,7) ) ,12) ) +((((transpose((X|X) ,-7) +transpose(transpose((X|X) ,-7) ,7) ) +transpose(((transpose(X,4) |transpose(X,-5) ) +echo(transpose(X,-5) ,4,6) ) ,12) ) +transpose((transpose(step(transpose((X+transpose(X,7) ) ,-5) ,12) ,-7) +transpose(shuffle(((X+X) +transpose((X+transpose(X,7) ) ,7) ) ) ,12) ) ,4) ) +transpose(transpose(step(((X+transpose(X,4) ) +transpose(X,7) ) ,12) ,-7) ,7) ) ) ) +transpose((((transpose(((echo(X,4,6) +transpose((X+X) ,4) ) +transpose(transpose(X,-7) ,7) ) ,4) +transpose(echo((X+(X|X) ) ,4,6) ,4) ) +transpose(echo(transpose(X,-5) ,4,6) ,7) ) +transpose(((step(X,12) +(X+transpose(X,7) ) ) |step(X,12) ) ,12) ) ,7) ) +(transpose(transpose(transpose(transpose(transpose(X,4) ,4) ,4) ,-5) ,-5) +transpose(arpeggio(((transpose((X|(echo(arpeggio(X) ,4,6) +transpose(X,4) ) ) ,4) +transpose((((echo(shuffle(X) ,4,6) +transpose(((X|X) +X) ,4) ) +transpose(transpose(X,-5) ,7) ) +(((((X+transpose(X,4) ) +transpose(X,7) ) +transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,7) ) |(X|X) ) +transpose(transpose(transpose(transpose(X,-7) ,4) ,4) ,-5) ) ) ,12) ) |((transpose((echo(((transpose((X+transpose(X,12) ) ,4) +transpose(X,4) ) +transpose(transpose(X,4) ,7) ) ,4,6) +((X|X) +transpose(X,-5) ) ) ,-5) +transpose(transpose(step(transpose(shuffle(X) ,4) ,12) ,-7) ,4) ) +transpose(echo((step(X,12) +transpose(X,-5) ) ,4,6) ,7) ) ) ) ,12) ) ) ) ,-7) |(transpose(echo(transpose(transpose(((arpeggio((echo(X,4,6) +(transpose(X,-5) |((X+transpose(X,4) ) +transpose(X,7) ) ) ) ) +transpose((transpose(transpose(X,-5) ,4) +transpose((X+transpose(transpose((X+transpose(X,7) ) ,-5) ,12) ) ,12) ) ,4) ) +(transpose((transpose((X+transpose(X,-7) ) ,4) |transpose((X+transpose(X,7) ) ,-5) ) ,4) +transpose(transpose((transpose(((((X+transpose(X,4) ) +transpose(X,7) ) +transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,4) ) +transpose((X+X) ,7) ) ,-7) |echo(shuffle((shuffle(X) +transpose(X,12) ) ) ,4,6) ) ,4) ,12) ) ) ,4) ,-5) ,4,6) ,-7) +transpose(transpose(transpose(transpose((echo(shuffle(transpose((((X+transpose(X,4) ) +transpose(X,7) ) +X) ,-5) ) ,4,6) +transpose(echo(transpose((X+transpose(X,12) ) ,4) ,4,6) ,7) ) ,-5) ,-5) ,-7) ,12) ) ) |arpeggio((echo((transpose(transpose(echo(shuffle((transpose(X,4) +transpose(X,7) ) ) ,4,6) ,-5) ,-5) +step(transpose(((step(((X+transpose(X,4) ) +transpose(X,7) ) ,12) +transpose(echo((X|X) ,4,6) ,7) ) +transpose(((X+X) |transpose(X,-7) ) ,7) ) ,-7) ,12) ) ,4,6) +transpose(transpose((transpose((echo((X|X) ,4,6) |(transpose(transpose((X+X) ,4) ,-7) +transpose(transpose(transpose(transpose(X,4) ,4) ,-5) ,12) ) ) ,-5) +transpose((transpose(echo((transpose(X,4) |transpose((((X+transpose(X,4) ) +transpose(X,7) ) |(X|X) ) ,-7) ) ,4,6) ,4) +transpose(transpose(X,4) ,7) ) ,7) ) ,-5) ,-7) ) ) ) )
random seed used was 23

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