superimpose :: (Pattern a -> Pattern a) -> Pattern a -> Pattern a
superimpose plays a modified version of a pattern 'on top of' the original pattern, resulting in the modified and original version of the patterns being played at the same time. For example this:
d1 $ superimpose (fast 2) $ sound "bd sn [cp ht] hh"
...is the same as this:
d1 $ stack [sound "bd sn [cp ht] hh", fast 2 $ sound "bd sn [cp ht] hh" ]