This is a discussion on How loud was a Civil War battlefield? within the Military History forums, part of the Armed Services category; (I'm just talking round numbers here - not trying to do an exact computation. Be gentle.)
Assume a man could fire a sustained three rounds ...
(I'm just talking round numbers here - not trying to do an exact computation. Be gentle.)
Assume a man could fire a sustained three rounds per minute.
A Civil War regiment typically was formed with 1,000 men so that would mean one full regiment could fire 3,000 rounds per minute. So roughly equivalent to a .58 caliber mini-gun firing 500 grain bullets (over 200 pounds of lead going downrange each minute).
The XII Corps at Gettysburg had about 17,000 men present for duty there. So maybe they had only 10,000 combat soldiers on Culp's Hill (where the real fighting was - not Little Round Top). That would be 30,000 rounds per minute. According to after action reports Geary's 2nd division (the smallest of the three in XII corps) fired 227,000 rounds just on the 3rd day.
Multiply that by all of the Corps at Gettysburg, and add in artillery. And Confederate fire.
Let's not forget about the screams of agony and death. Add to that the screams of encouragement and orders to advance or retreat. Surely the entire field of combat was one of confusion and turmoil. But most of us have endured our own experiences in the fog of war, though not to the degree I suspect of those in such large formations.
To roughly answer Samuels question. Blank charges are usually about half as loud as live fire, the reason is a lighter powder charge and no projectile. I will say that the big howitzer up at Fort Meigs in Ohio can set off car alarms at 200 yards with just a blank charge. In battle artillery lends class to what otherwise would be a common brawl.
I have done a few reenactments with only a few hundred reenactors and some cannons. It is loud and I can only surmise what a real battle would be like, but it sure would have been loud. Even with blank charges you can really feel the concussion from the cannons.