"Delete notes" is much faster (presumably because the number of notes is usually much lower than the number of CCs, if an item has lots of CC expression).
"Delete all notes of the less than X" can get a bit slow if the number of small notes is unusually high, but since it only affects the active take, it doesn't completely freeze REAPER. However, if this action is ever expanded to all editable takes, the slowness may cause trouble.
|