> If you manually did enough work have the copyright it is fine.
Amount of work is not a basis for copyright. (Kind of work is, though the basis for the “kind” distinction used isn't actually a real objective category, so its ultimately almost entirely arbitary.)
That could get tricky. A lot of hardware and software MIDI sequencers these days have probabilistic triggering built in, to introduce variation in drum loops, basslines, and so forth. An argument could be made that even if you programmed the sequence and all the sounds yourself, having any randomization or algorithmic elements would make the resulting work ineligible for copyright.
Amount of work is not a basis for copyright. (Kind of work is, though the basis for the “kind” distinction used isn't actually a real objective category, so its ultimately almost entirely arbitary.)