The earl of Derby took six minstrels with him on his two expeditions to Prussia in 1390-93: two trumpeters, three pipers and a nakerer in the first expedition, three trumpeters and three pipers in the second. The three kinds of instruments are typical of those shown used by musicians accompanying soldiers in manuscript illustrations of the 13th to 15th centuries. Several pictures from Le chroniche di Giovanni Sercambi ASL MS.107, 1368-1424, show a musician at the head of a column of infantry playing a pipe and tabor.
Froissart reports trumpets being used to signal alarm, command attention for orders, and command attack and retreat. By this time civilian huntsmen like William Twyti knew at least six different horn calls, each with a different meaning, and military trumpeters may have had at least as complete a vocabulary.
Machiavelli wrote in 1521 about commands also being given by pipe and drum as common practice in his time, and later fife and drum were used to deliver a rich vocabulary of battlefield and camp commands. I don't know how long before 1521 the practice began.
There is a lot we don't know.