If I'm reading right, key velocity affects attack and, at some mod wheel settings, timbre of the brass instruments in GPO. What I've never seen (it might be there, but I haven't found it yet) is a chart/detail of the relationship between velocity/mod wheel and attack/timbre. Is there such a write-up, or at least some general relationship info somewhere? I could probably figure it out with my hands and ears, but I'd rather not re-invent the wheel if I can avoid it.