Gavin Bryars on Tune Percussions
"Tune percussions are so-called keyboard percussions: marimbas, vibraphones, glockenspiels, and so on. Those which are capable of playing definite pitches and therefore melodic material. The ways in which they can combine and the ways they can give colour within any given harmony is particularly rich. Each one will set up a different kind of overtone structure. The xylophone and the marimba look remarkably similar but the tuning is slightly different in terms of the overtones they generate. When combined in different ways you can get surprisng results. Then, if you interject other instruments with that, these instruments combine vertically to produce very rich sounds. Similarly you can make a transition from one set of instruments to another imperceptibly. The piece for Nexus starts with untuned percussion: drums, little instruments which don't advertise pitch, and gradually tuned instruments come in underneath. The transition from one form of percussion to another and the ways in which it's possible to blur those distinctions is quite interesting."