I've seen this some three times on the intervebs and it always hits me how effortless it is to make it sound sweet. I think there's also something about how it's set up to mimic the progression of songs in just how the user paces themselves. First one sound, then another, then a third, then the first changes, then one is removed, then you shuffle it all up for the chorus. It makes it intuitive induce enough variety and complexity by going with the flow.

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Using Tetris pieces to make a track is beautiful too.

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I broke it.