What is the difference between the mechanical and electrical couplers in PAB?
On the real organ the mechanical couplers make a mechanical connection between the keyboard (the keys on different keyboards move together when the coupler is engaged), while the electrical couplers make an electrical connection without a joint key movement. In the PAB Professional and Extended Editions, the electrical and mechanical couplers only have a visual difference, their operation is the same. In PAB Gravissimo, the electrical couplers are coupling between the divisions (i.e., Great, Positive, etc.) while the mechanic couplers connect keyboards (i.e., I, II, III, etc.). Since in PAB Gravissimo you can assign different divisions to different keyboards and change this assignment while you play, the couplers will work differently. Both electric and mechanical couplers are available for use whichever you prefer.