All previous answers have been spot on. One extra point about musicians is that all ten companies in a battalion had their own, one drummer each at the start of the war (plus two fifers for the grenadier company), and two per company after the augmentation of August 1775 that increased each company by one sergeant, one drummer and 18 privates (the number of fifers remained the same). There is no clear evidence, but it seems most likely that one of the light company drummers was taught to play the hunting horn, forerunner of the bugle in Napoleonic times, but was still referred to as a "drummer" on the muster rolls (as were the grenadier fifers in most regiments). Arthur is correct in that the grenadier musicians could be grouped together, but the light bobs tended to retain their own drummers/hornists. Each type of battalion would appoint the senior drummer as "drum major" and that man would attend the battalion CO.
Bear in mind that, following unofficial practice in the F&I War, British troops in the AWI tended to have orders passed solely by word of mouth. This was finally acknowledged officially in 1778, by an order from the C-in-C, Baron Amherst