Jim Nielson’s blanket term for experiments in which an entire recorded track of music is programmatically processed using computer algorithms, for instance speeding up a track, slowing it down, pitching it up or down, cutting or duplicating beats or measures systematically, etc. (If anyone knows a blanket term already in use for these practices, please let me know!)
Long before computers, people enjoyed playing singles meant to be played on turntables at 45 rpm at the LP speed of 33 1/3 rpms, and vice versa. With computers it is possible to programmatically slow down or speed up tracks whatever amount you like.
Nightcore is a subculture that creates “new” music by speeding up and pitching up techno and trance dance music, usually without any further manipulation or creative additions. Chopped and screwed is a hip hop djing and production technique that usually starts by slowing tracks down to 60-70 bpm (beats per minute) before then “chopping” and “screwing” the music in varous ways.
Probably the most notable practitioner of the more complex “beat swaps” style of reprocessing is Adam Emond. The genre is a kind of musical form of the YouTube Poop phenomenon known as “replacement remixes” (x but every time it says y, z). Perhaps it owes its inspiration to the chopped and screwed school of djing and production developed in southern hip hop, where complex beat manipulation occurs to create new music.
A related set of experiments, though they undoubtedly require more direct manipulation and adjustments on the part of the remixer, are those that use digital techniques that change songs from major to minor keys and vice-versa (minor key songs tend to be sad, dark, or threatening; major key songs tend to be lighter and happier sounding).
Majorscaling is the more common practice. There’s a Facebook page devoted to these experiments.