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 18 generations the expression "X" became this:
((((((step(transpose((((echo(echo((X|X) ,4,6) ,4,6) |shuffle((arpeggio(transpose(X,-5) ) +((X+transpose(X,7) ) +transpose(X,12) ) ) ) ) +transpose(echo(((transpose(((step(X,12) +transpose(X,4) ) +transpose(shuffle(X) ,7) ) ,-5) +(X|(X|X) ) ) +transpose(transpose(transpose(X,-7) ,-7) ,4) ) ,4,6) ,4) ) +transpose((step(arpeggio(X) ,12) +transpose(step(X,12) ,4) ) ,7) ) ,-7) ,12) |shuffle(((transpose(echo((arpeggio(step(arpeggio(X) ,12) ) +X) ,4,6) ,-7) |(transpose(X,-7) +transpose(echo((transpose(X,-7) |transpose(X,-7) ) ,4,6) ,12) ) ) +transpose(echo(transpose(step((transpose(X,4) +transpose(transpose(X,-5) ,7) ) ,12) ,-5) ,4,6) ,12) ) ) ) +transpose(transpose(step(transpose((transpose(transpose(((X+X) |echo(X,4,6) ) ,-5) ,-5) |step((echo((X+transpose(X,7) ) ,4,6) |(((X+X) +transpose((transpose(X,-5) +transpose(X,4) ) ,12) ) +transpose(echo(transpose(X,-7) ,4,6) ,7) ) ) ,12) ) ,4) ,12) ,-7) ,7) ) +transpose(transpose((step((transpose((transpose(transpose(X,-5) ,-5) |step(transpose(X,-5) ,12) ) ,-7) |((((X+(X+X) ) +transpose((transpose(X,4) |(X+transpose(X,7) ) ) ,4) ) +transpose(((X+transpose(X,12) ) |X) ,7) ) |((X+X) +(X+transpose(X,7) ) ) ) ) ,12) |step((((transpose(echo((((X+X) +transpose((X+transpose(X,7) ) ,4) ) +transpose(X,7) ) ,4,6) ,4) +transpose(X,7) ) |(echo(transpose(transpose(X,-7) ,-7) ,4,6) +transpose(transpose(arpeggio(transpose(X,-5) ) ,-7) ,4) ) ) +transpose(((X|X) |(X|X) ) ,4) ) ,12) ) ,-5) ,12) ) +transpose((((transpose((((transpose(((transpose((X+transpose(X,12) ) ,-5) |transpose((((X+transpose(X,7) ) +transpose(X,4) ) +transpose(X,7) ) ,-7) ) +transpose(((X+transpose(X,7) ) +transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,12) ) ,-5) ) ,-7) +((((transpose(transpose(transpose(X,-5) ,-5) ,-7) +transpose(((shuffle(X) +transpose(((X|X) |(X+transpose(X,12) ) ) ,12) ) |transpose(X,-7) ) ,4) ) +transpose(shuffle(((X+transpose(X,12) ) +(transpose(X,-5) +(X+transpose(X,12) ) ) ) ) ,7) ) |arpeggio((((shuffle(X) +transpose((X|X) ,12) ) +transpose(transpose(echo(X,4,6) ,-5) ,4) ) +transpose((shuffle(X) +transpose(transpose(X,-5) ,7) ) ,7) ) ) ) |((step((echo(transpose(X,4) ,4,6) |echo(transpose(X,4) ,4,6) ) ,12) +transpose(shuffle(transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,4) ) ,4) ) +transpose((arpeggio(transpose(X,4) ) +transpose(shuffle(X) ,12) ) ,7) ) ) ) +transpose(echo(transpose((((transpose(X,-5) +transpose(step(transpose(X,-7) ,12) ,12) ) +transpose((shuffle(transpose(X,4) ) +arpeggio(X) ) ,12) ) +transpose(((X+transpose(X,4) ) +transpose(transpose(X,4) ,7) ) ,12) ) ,-5) ,4,6) ,4) ) +transpose((shuffle(((arpeggio((X+transpose(X,12) ) ) +transpose(X,-7) ) |transpose(transpose(X,-7) ,-5) ) ) |(((transpose(step(X,12) ,4) +(X+transpose(X,12) ) ) |(((X+transpose(X,4) ) +transpose(X,7) ) +transpose(echo(X,4,6) ,4) ) ) |transpose(transpose(X,4) ,4) ) ) ,7) ) ,4) |transpose(arpeggio((transpose(step(transpose(X,4) ,12) ,-5) |step(transpose(shuffle(X) ,-7) ,12) ) ) ,-7) ) +transpose((transpose(transpose((transpose((echo(step(X,12) ,4,6) +transpose(((X+transpose(X,7) ) +transpose((X|X) ,7) ) ,12) ) ,4) +transpose((X+X) ,-7) ) ,-7) ,-5) +transpose(echo(((shuffle(transpose((transpose(X,-7) +transpose((shuffle(X) +transpose((X+X) ,12) ) ,-7) ) ,4) ) |((echo(((((X+transpose(X,4) ) +transpose(X,7) ) +transpose(X,4) ) +transpose(shuffle(X) ,7) ) ,4,6) |(transpose((X+transpose(X,7) ) ,-5) |((arpeggio(X) +transpose(step(X,12) ,7) ) +transpose(transpose(X,4) ,12) ) ) ) +arpeggio(echo(transpose(arpeggio(X) ,-5) ,4,6) ) ) ) +transpose(transpose(transpose((X+X) ,-7) ,4) ,7) ) ,4,6) ,7) ) ,4) ) +transpose(step((transpose(step((transpose(transpose(X,-7) ,-5) |step(step((X+transpose(X,12) ) ,12) ,12) ) ,12) ,4) |(((arpeggio((((X+X) +(X|X) ) +(transpose(X,-7) +transpose(transpose(X,-5) ,12) ) ) ) +transpose(transpose(((X|X) +X) ,-5) ,-5) ) +(echo((transpose(arpeggio(arpeggio(X) ) ,-5) +transpose(((X|X) +transpose(shuffle(X) ,7) ) ,12) ) ,4,6) +transpose((transpose(((step(X,12) +transpose(X,4) ) +transpose((X+transpose(X,12) ) ,7) ) ,4) +transpose(transpose(arpeggio(X) ,4) ,-5) ) ,12) ) ) +transpose(transpose(X,-7) ,12) ) ) ,12) ,7) ) ,4) ) +transpose((transpose(transpose((transpose(transpose(((transpose(shuffle(X) ,-7) +(X+X) ) +transpose((transpose(transpose(X,4) ,-7) +transpose(((((X+transpose(X,4) ) +transpose(X,7) ) +transpose((X+X) ,4) ) +transpose(X,7) ) ,7) ) ,12) ) ,4) ,-5) +transpose((shuffle(((X+transpose(X,-5) ) +step(X,12) ) ) +(echo(X,4,6) +transpose((((arpeggio(X) +step(X,12) ) +transpose(transpose(transpose(X,-5) ,4) ,4) ) +transpose(transpose(X,-5) ,7) ) ,4) ) ) ,12) ) ,4) ,4) +transpose(((transpose((echo(((X+transpose((X|X) ,12) ) |X) ,4,6) |((step(arpeggio((shuffle(X) |(((X+X) +transpose(transpose(X,4) ,4) ) +transpose(X,7) ) ) ) ,12) |((echo(X,4,6) +arpeggio(X) ) +transpose(transpose(echo(X,4,6) ,-5) ,7) ) ) +transpose((((((X|X) +transpose(step(arpeggio(X) ,12) ,4) ) +transpose(shuffle(X) ,7) ) |(X+transpose(echo(X,4,6) ,7) ) ) |((arpeggio(transpose(X,-5) ) +transpose(transpose(step(X,12) ,-5) ,7) ) |(transpose(X,4) +transpose(transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,-5) ,12) ) ) ) ,7) ) ) ,4) +transpose(((step((transpose((X+X) ,4) +transpose(((X+transpose(transpose(X,-7) ,7) ) |((step(X,12) +transpose(step(transpose(X,-7) ,12) ,4) ) +transpose(X,7) ) ) ,7) ) ,12) +transpose(arpeggio(step(echo((X+transpose(transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,-5) ,7) ) ,4,6) ,12) ) ,12) ) +arpeggio(((step(X,12) +(transpose(((X+X) +transpose(X,-5) ) ,4) +transpose(transpose((X|X) ,4) ,12) ) ) +transpose(transpose(transpose(((((X+transpose(X,4) ) +transpose(X,7) ) +transpose(X,7) ) +transpose(arpeggio(X) ,12) ) ,-7) ,-7) ,12) ) ) ) ,4) ) +transpose(echo((transpose(shuffle(((arpeggio(transpose(X,4) ) +transpose((X+X) ,7) ) +shuffle(X) ) ) ,-5) |((transpose(X,-7) +transpose(X,7) ) +echo(echo(transpose(X,-7) ,4,6) ,4,6) ) ) ,4,6) ,7) ) ,12) ) ,7) ) +((shuffle(((transpose((((step(transpose((X+(X|echo(transpose(X,-5) ,4,6) ) ) ,4) ,12) +transpose((arpeggio(transpose((((step(X,12) +((X+transpose(X,4) ) +transpose(X,7) ) ) +(X+X) ) +echo(X,4,6) ) ,-5) ) |(transpose(transpose(((X+X) +transpose(X,7) ) ,-5) ,4) +((transpose(transpose(X,-7) ,-5) +transpose(shuffle((X+transpose(transpose(X,4) ,7) ) ) ,12) ) +step(transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,4) ,12) ) ) ) ,7) ) +transpose((((((((((step(X,12) +transpose(transpose(step(X,12) ,-7) ,4) ) +transpose(((X+transpose(X,12) ) +transpose((X|X) ,12) ) ,7) ) +transpose(X,4) ) +transpose((arpeggio(X) +transpose(transpose(arpeggio(X) ,-7) ,7) ) ,7) ) +transpose(transpose(transpose((shuffle(X) +transpose(echo(X,4,6) ,12) ) ,4) ,4) ,4) ) +transpose(step((arpeggio((X+transpose(transpose(X,4) ,12) ) ) +transpose(transpose(shuffle(X) ,-5) ,4) ) ,12) ,7) ) +transpose((transpose(X,4) +transpose(transpose(arpeggio(X) ,-7) ,12) ) ,4) ) +(transpose(((transpose(shuffle(X) ,-7) +transpose(X,4) ) +transpose(transpose(((X+transpose(X,7) ) |((X+transpose(X,4) ) +transpose(X,7) ) ) ,-5) ,7) ) ,-7) +transpose((transpose(transpose(X,-7) ,-5) |(X+transpose(X,7) ) ) ,12) ) ) +transpose((transpose((step(echo(shuffle(X) ,4,6) ,12) +shuffle((X|X) ) ) ,-7) +((transpose(transpose(transpose(X,-7) ,-5) ,4) +transpose(transpose(shuffle(transpose((transpose(X,-7) |(shuffle(X) |step(X,12) ) ) ,-5) ) ,4) ,7) ) +transpose((transpose(((transpose(transpose(X,-7) ,-7) |(X+transpose(shuffle(X) ,12) ) ) |echo(transpose(transpose(X,-7) ,-5) ,4,6) ) ,4) +transpose(transpose(((((X+transpose(X,7) ) |step(X,12) ) +transpose(arpeggio(transpose(X,-5) ) ,4) ) +transpose(((X|X) |(X+X) ) ,7) ) ,4) ,-7) ) ,7) ) ) ,12) ) ,4) ) +transpose((transpose(transpose(((transpose(X,-5) +transpose(((X+transpose(X,4) ) +transpose(X,7) ) ,4) ) +transpose(X,7) ) ,4) ,-7) +(transpose(transpose((X+X) ,-5) ,4) |(transpose(X,4) |arpeggio(X) ) ) ) ,7) ) ,4) +transpose(((transpose((transpose(step(X,12) ,-7) +transpose(transpose(shuffle(X) ,-5) ,12) ) ,4) |transpose(echo((transpose((X+X) ,4) |(transpose(transpose(X,4) ,4) +transpose(transpose((transpose(X,4) +echo(X,4,6) ) ,-5) ,12) ) ) ,4,6) ,4) ) |arpeggio(echo((transpose(transpose(((X+transpose(X,12) ) +transpose(transpose(X,-7) ,7) ) ,-5) ,-5) +((transpose(transpose(X,4) ,-5) +transpose(transpose(step((X|X) ,12) ,4) ,4) ) +transpose(((((X|X) +transpose(shuffle(X) ,4) ) +transpose(transpose(X,4) ,7) ) +transpose(transpose(transpose(arpeggio(X) ,-7) ,-7) ,12) ) ,7) ) ) ,4,6) ) ) ,4) ) +transpose(echo((transpose(transpose(transpose((shuffle(transpose(X,-7) ) +X) ,-5) ,4) ,-5) +transpose(transpose((((X+transpose(X,12) ) +((X+X) +transpose(X,4) ) ) +((arpeggio((X+transpose((X+X) ,12) ) ) +transpose(shuffle(transpose(transpose(X,-7) ,-5) ) ,12) ) +transpose((X+transpose(X,12) ) ,-5) ) ) ,-5) ,12) ) ,4,6) ,7) ) ) +shuffle(transpose(transpose((echo(((transpose(X,-5) +transpose(transpose(transpose((step(X,12) |X) ,-7) ,-5) ,12) ) +transpose(transpose(transpose(transpose(transpose((((X+transpose((X+X) ,12) ) +transpose(shuffle(shuffle(X) ) ,4) ) +transpose(((X+transpose(transpose(X,-7) ,4) ) +transpose(transpose(X,4) ,7) ) ,7) ) ,4) ,-7) ,-7) ,4) ,7) ) ,4,6) +transpose((((arpeggio((shuffle(X) |step(echo(X,4,6) ,12) ) ) +transpose(transpose(((X+X) +transpose(step(X,12) ,12) ) ,-7) ,12) ) +transpose(transpose((arpeggio(((((X+X) +transpose(step(X,12) ,4) ) +transpose(X,7) ) +((X+transpose(X,-5) ) +(X+(X+transpose(X,7) ) ) ) ) ) +transpose(echo(transpose(((echo((X+transpose(X,7) ) ,4,6) +transpose(step(transpose(X,-5) ,12) ,4) ) +transpose((X|transpose(X,-5) ) ,7) ) ,4) ,4,6) ,12) ) ,4) ,7) ) +transpose((((transpose((echo(echo(X,4,6) ,4,6) +(X+X) ) ,4) +transpose(step(((X+step((X+X) ,12) ) |transpose(X,-7) ) ,12) ,7) ) +transpose(transpose(((((X+transpose(X,12) ) +transpose(X,12) ) +transpose((X+transpose(X,12) ) ,4) ) +transpose(((X|X) +X) ,7) ) ,-7) ,4) ) +transpose(((echo(arpeggio((step(X,12) |shuffle(X) ) ) ,4,6) +transpose(((X|X) |step((X|X) ,12) ) ,-7) ) +transpose(transpose(transpose(transpose(transpose(transpose((X|X) ,4) ,-5) ,-7) ,4) ,4) ,12) ) ,12) ) ,7) ) ,7) ) ,-5) ,-5) ) ) +transpose(transpose(echo(step(transpose(transpose((transpose(transpose(((X|X) |(X+X) ) ,4) ,4) |transpose(transpose(transpose(X,-7) ,-5) ,-7) ) ,4) ,-7) ,12) ,4,6) ,4) ,-5) ) )
random seed used was 144083186

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