Thanks a lot to everybody for sharing your knowledge about factory styles' production. The motivation for my question was: I find it very hard to create a style (from scratch, from the keyboard itself and from the recording/editing tools provided) that has a quality comparable to the factory styles included in my Ketron module. So the factory must have tools (and colaboration of professional musicians, like Andrea suggests) that we'll never possess, no matter how talented we are. I can understand that midi real instruments played by experienced musicians will produce styles difficult to match in quality, with our keyboards.

Thanks
José.