"In some of the early 125th reenactment like Gettysburg in 1988 this noise factor was impressed on me. Standing in open fields the noise was so great that no one could hear the Officers commands. They would yell as loudly as they could. To be repeated by the file closers, which was picked up and repeated again by the men in the rear ranks so that everyone would know what the order was. The thing was it was even hard to hear the man yelling right behind you."
There have been posts on the site about the use of whistles to give audible commands. The high pitch might have been distinguishable from the sounds of battle. Conversely, it is common for someone involved in a gun fight not to have heard the shots fired. When on the firing line in a rifle match, it is possible to concentrate so much you don't even hear your own weapon's report. Human brains are marvelous in their reaction to certain stresses. Stan