However, sometimes a hand held microphone can be passed around the room to pick up the voices of participants located too far away from the PZM microphones installed in the desk at the videoconferencing operator's position. Finally, the processing of the audio signal is the last link in the chain of audio processing that is important in videoconferencing. A high quality videoconference system is what is called in data transmission terminology, full duplex instead of simplex. Two way radio is a good example of simplex communications as only one party can talk at a time. One frequency is used to transmit and receive information.
Duplex communication is similar to a telephone conversation.
Two or more frequencies are used and two people can talk at once or interrupt each other. There is a great deal of audio processing taking place in which the frequencies used in the data transmission are compressed and processed and then reexpanded at the receiving site. With all of this processing taking place, there is a big difference in the levels of success of different manufacturer's methods to transmit the discussion of the participants. The intelligibility is better in some systems due to faster audio switching in the duplex mode or because a better microphone is used with a more effective design.