IC Realtime H.264E Hybrid DVRs 4/8/16-CH Analog + 4/8/16-CH IP - Manual (Page 29)

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Figure 3-2
3.7 Connecting Audio Input & Output, Bidirectional Audio
3.7.1 Audio Input
BNC port is adopted for audio input port.
Due to high impedance of audio input, please use active sound pick-up.
Audio transmission is similar to video transmission. Try to avoid interference, dry joint,
loose contact and it shall be away from high tension current.
Figure 3-3
3.7.2 Audio Output
The audio output signal parameter is usually over 200mv 1KΩ (BNC). It can directly
connect to low impedance earphone, active sound box or amplifier-drive audio output
device.
If the sound box and the pick-up cannot be separated spatially, it is easy to arouse
squeaking. In this case you can adopt the following measures:
z
Use better sound pick-up with better directing property.