Definition: A program channel carries the accompanying audio. If feeding a stereo system, there will, of course, be two audio channels. It may also imply what are called cue and coordination channels. A cue channel is used by a program director or producer to manage her/his people at the distant end. It is just one more audio channel. A coordination channel is a service channel among TV technicians.
Composite transmission normally is used on TV broadcast and community antenna television (CATV or cable TV) systems. Video and audio carriers are "combined" before being fed to the radiating antenna for broadcast. The audio subcarrier is illustrated in Figure 16.6 in the composite mode.
For point-to-point transmission on coaxial cable, radiolink, and earth station systems, the audio program channel is generally transmitted separately from its companion video providing the following advantages:
• It allows for individual channel level control.
• It provides greater control over crosstalk.
• It increases guardband between video and audio.
• It saves separation at broadcast transmitter.
• It leaves TV studio at separate channel.
• It permits individual program channel preemphasis.
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