Here is the factory default note number assign map for the HPD-20's pads:
M1 = 60
M2 = 61
M3 = 62
M4 = 63
M5 = 64
S1 = 65
S2 = 66
S3 = 67
S4 = 68
S5 = 69
S6 = 70
S7 = 71
S8 = 72
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If you'd like to change the Note Number assignments, click the following link for further instructions.
Handsonic HPD-20: Assigning MIDI Note Numbers to the Pads