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Many Axis network video products do not come with a built-in speaker. An active speaker—
a speaker with a built-in amplifier—can be connected directly to a network video product with
audio support. If a speaker has no built-in amplifier, it must first connect to an amplifier, which
is then connected to a network camera/video encoder.
To minimize disturbance and noise, always use a shielded audio cable and avoid running the cable
near power cables and cables carrying high frequency switching signals. Audio cables should also
be kept as short as possible. If a long audio cable is required, balanced audio equipment—that is,
cable, amplifier and microphone that are all balanced—should be used to reduce noise.
8.3
Audio modes
Depending on the application, there may be a need to send audio in only one direction or both
directions, which can be done either simultaneously or in one direction at a time. There are three
basic modes of audio communication: simplex, half duplex and full duplex.
8.3.1 Simplex
Figure 8.3a In simplex mode, audio is sent in one direction only. In this case, audio is sent by the camera to the
operator. Applications include remote monitoring and video surveillance.
Figure 8.3b In this example of a simplex mode, audio is sent by the operator to the camera. It can be used, for
instance, to provide spoken instructions to a person seen on the camera or to scare a potential car thief away from a
parking lot.
LAN/WAN
Audio sent by camera
Video sent by camera
PC
Network camera
Loudspeaker
Microphone
LAN/WAN
Audio sent by operator
Video sent by camera
PC
Network camera
Loudspeaker
Microphone
AUDIO - CHAPTER 8
