Based on what I've read, we can possibly narrow the role of Mr. Beall to a fifer or drummer. Supposedly the bugle is more associated with cavalry or artillery, while the fife and drum connect more with infantry. Furthermore, the drum was much more common than the fife.
A bugler could be found attached to a commander in battle, giving orders to the soldiers since his instrument could be heard above the musket fire and noise of war. The fife and drum were difficult to hear in battle however, and since many of these musicians were under age, they were often sent to the rear for ambulance duty during the times of direct fighting.
According to William's death certificate, he was a son of Elias H. Beall.