Whoops - I tried using the search function but nothing came up. Didn't realise there'd been a recent thread already.
In Cubase, it's under Project Setup (where you set the bit depth etc.) and basically it adjusts the attenuation for when you pan from left to right. At 0dB, sounds in the center appear louder than they do at either side, and the panning law compensates for that somewhat.
I think that's right, anyway, but if someone wants to correct me on that then feel free.