Hello everyone -
I did a tutorial on this some time back; it was involved, convoluted, and confusing. I understood it (most of the time) but I don't think anyone else did. Here's a reworking, straightforward and more briefer :
GPO figures pan as a percentage left or right from top center.
Sibelius pan works like a protractor, with zero at hard left where zero degrees would be, 127 at hard right where 180 degrees would be, and the mid-point, 63.5 steps, at 90 degrees top center.
Coordinating Sibelius pan with GPO means taking Sib's top center point, 63.5 steps, as 100%, and figuring from that.
For instruments on the left, the GPO percent must be subtracted from 100% to get you to the left side of the Sibelius pan. For example, Piccolo NV loads with a pan of 20% left. 20% left in Sibelius means 20% less than (left of) the 63.5 top center point. 100% - 20% = 80%. Take 80% of 63.5 to get the correct left side midi position in Sibelius: 0.8 X 63.5 = 50.8, rounded up to 51.
For instruments on the right, GPO percent must be added to 100% to get you to the right side of the Sibelius pan. For example, Tenor Trombone Player 1 loads with a pan of 25% right. 25% right in Sibelius means 25% more than (right of) the 63.5 top center point. 100% + 25% = 125%. Multiply by 63.5 to get the correct right side midi position in Sibelius: 1.25 X 63.5 = 79.375, rounded down to 79.
Hope this helps.