Transposing MIDI
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A whole region, or multiple regions, can be transposed at once, with the help of the Transpose MIDI dialog, accessed by right clicking a region > name_of_the_midi_region > MIDI > Transpose… .
This very simple dialog allows to choose either a number of semitones to add or subtract to all the notes inside the region(s), and/or for more significant changes, octaves (12 semitones).