Each pad on the SPD-SX has its own note number assigned from the factory. Here are the factory assignments:
PAD 1 = 60
PAD 2 = 61
PAD 3 = 62
PAD 4 = 63
PAD-5 = 64
PAD-6 = 65
PAD-7 = 66
PAD-8 = 67
PAD-9 = 68
Trigger Input 1/2 = 69/70
Trigger Input 3/4 = 71/72
Tip: These note number assignments can be changed if desired. See information in the following link for instructions about changing them:
Assigning MIDI Note Numbers to the Pads