Apple Logic Pro 9 - Manual (Page 1049)

Understanding How MIDI Events and Apple Loops Are
Transposed
Transposition events (and their chord counterparts) pitch-shift MIDI events and
Apple Loops.
MIDI Events
Transposition events change the actual MIDI events themselves. For example, if you create
a MIDI region that contains a C3 note event, copy the MIDI region, and then create a
transposition event of +2 at the start of the copied MIDI region, the transposition event
changes the note event to a D3.
Despite this data change to events, the Transposition track works nondestructively, as
you can change the transposition of MIDI events multiple times. Imagine you copy the
D3 of the example above to a position where the Transposition track is set to +2; the
MIDI event will be played back as D3. But if the Transposition track is set to a different
playback interval at the target position, the MIDI event will be pitch-shifted to the new
playback transposition.
1049 Chapter 35 Editing Transposition with the Chord and Transposition Tracks