The programmers for the factory styles use a computer program for creating styles. The keyboard itself is rarely, if ever, used.
I had some converted Korg styles sent to me and I thought the idea behind them was excellent, as they are programmed over at least
8 bars, which tends to allow for some nice variation within a style section.
Programming from scratch on the keyboard is very tedious and requires a more than good knowledge of how each part (bass, chords, pads etc.) is played idiomatically, and this must be done for each variation (4) plus each fill-in as well....not to forget intros and endings, which are programmed slightly different from the other sections.
One thing I did learn from the Korg styles was making each variation of my own
Frankenstyles at least 8 bars long, and to search for donor parts from other styles that had some sort of movement in them. I have a folder with styles that are used for just that purpose.
I find it much easier and quicker (with genuinely great results) to use the
Style Assembly section of Yamaha's Style Creator and swap in parts from other styles, which eliminates a lot of the hassles of playing in the parts "live", which will involve setting note limits, and triggering types...when using donor parts, these settings are already done for you.
Also, in Yamaha;s style creator there is a
Groove & Dynamics section which is extremely handy for changing the "feel" of a style (adding "swing" for instance) or making parts from other styles blend in (I'm sure Korg has an equivalent feature)....also, in the more current Yamaha style creators, the guitar parts can be set for stroke or arpeggio (or "all-purpose"), giving some very impressive results.
So, Mark, even without programming from scratch, you can do a lot to a style to make it your own, and the more time you spend on editing, the easier it becomes.
Ian