I didn't know what a Capsule Communicator was, I thought it was a piece of equipment used by astronauts in their space capsule. But it's a role if the ground crew; the person who is responsible for communicating with the astronauts.

Knowing that, the article makes more sense. Mission control has to send audio to transmit and also turn the transmitters on and off. They do that all in one data line (phone line) using these tones.