what is with all the numbers on the screen

In the listening center where Sgt. Duffy is in charge, the listeners seem to be typing in numbers on their screens, but the listener who is going off-duty mentioned the soldier talking about his hot wife, so he must have been listening to a human conversation. How did the conversation turn into numbers on the screen? Did the listeners recode the conversations into numbers? And later, when they dispatch a jet to pickup the audio tapes containing "the target is destroyed," why didn't they hear that audio at their facility? Were they just out of range?