In De musica I.2, Boethius describes 'musica instrumentis' as music produced by something under tension (e.g. strings), by wind (e.g. aulos), by water, or by percussion (e.g. cymbals). Boethius himself doesn't use the term 'instrumentalis', which was used by Adalbold II of Utrecht (975–1026) in his Epistola cum tractatu. The term is much more Common in the 13th century and later. It is also in these later texts that musica instrumentalis is firmly associated with audible music in general, including vocal music. Scholars have traditionally assumed that Boethius also made this connection, possibly under the header of wind instruments ("administratur ... aut spiritu ut tibiis" ), but Boethius himself never writes about "instrumentalis" as separate from "instrumentis" explicitly in his very brief description.