for a start anything above 5kHz (some would say 4kHz) is simply spectral harmonics for different instruments. SO it is not so much about having bright instruments as having a full-range of sounds and a little less (or no) lpf on everything - the upper harmonics of any instrument are what you find in the range above 10kHz, but mostly it is the stuff associated with open cymbals like rides and crash cymbals and open hi-hats