Audio communication is transmitted in a number of ways.
Simplex Audio
Audio is transmitted between two positions one way at a time, normally a button or switch needs to be selected to change the direction of the audio path. This mode of operation is also known as PTT (Press To Talk).
Switched Duplex
Audio is transmitted between two positions the same as Simplex Audio, but the equipment (Intercom Exchange) switches the direction of the audio automatically, the equipment senses which end is the loudest and switches the direction of the speech. This can be a problem where there is a high back ground noise level at one end of the communication e.g. air conditioning, machines in manufacturing, etc
Full Duplex Audio
Audio is transmitted in both directions simultaneously. Most phone systems use full duplex audio and this provides the possibility for a more natural two-way conversation. In Full Duplex loudspeaking systems, the onset of audio feedback (caused when both channels are open simultaneously) is delayed by dimming one channel whilst audio is passing through the second channel or by more sophisticated means involving the application of DSP(s).
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