There is confusion as to how command control was implemented for such batteries. Rawkins suggests 2 drummers were present, but this seems impractical when riding a wurst. A trumpeter apparently did not appear until well post-Napoleonic Wars. Digby-Smith's translation in SOJ of Smola suggests commands were given by word of mouth.
Grateful for thoughts and guidance.
The reason for relying on voice commands is the way the batteries were directed. France relied on its officers, so they used a drummer or later, bugler. The Austrians relied on their highly-trained NCOs. Each gun was run by an Oberfeuerwerker or sometimes, a Bombardier. Each pair of guns was directed by a Korporal and the battery was directed by an officer. So, there is a chain of command, rather than central direction.