Everyone is inside the ship when commands are issued so you would be able to hear them. If you are outside the ship's hull you would have some form of long range communication attached to your space suit. 

The Vigilance uses a simple loudspeaker system to issue commands on deck. It's simple, effective and with new technology they can easily broadcast messages to every inch of the ship.

One thing to note, since this was brought up before (by Latino, I believe.) Is that while on the ship, the Admiral is addressed to and referred to as Captain. However if you are going to say her name, it would be Admiral Chevalier not Captain Chevalier. She would be referred to as Admiral at all times when she is not on the ship, which will be almost never.