MIDI Editing : Real-Time Properties Settings : Duration : Duration Mode Pop-Up Menu
 
Duration Mode Pop-Up Menu
Select one of the following options from the Duration Mode pop-up menu: Set, Add, Subtract, Scale, Legato/Gap, or Legato/Overlap.
Set
Select to set notes to the specified duration.
Add
Select to add the specified duration to the current duration of each note.
Subtract
Select to subtract the specified duration from the current duration of each note.
Scale
Select to scale the current duration of each note by a percentage from 1 to 400%.
Legato/Gap
Select to extend each note to the following note. The specified duration is the subtracted to create a consistent gap between notes.
Legato/Overlap
Select to extend each note to the following note. The specified duration is then added to create a consistent amount of overlap.