1. Using occasions: Different microphones are used in different occasions. There are outdoor microphone, indoor microphone, Omni-directional microphone, unidirectional microphone, etc. 
   
2. Installation method: Such as ceiling installation, wall installation, desktop installation, hidden installation, etc. 
   
3. Some special industries: There has special requirement for some special industries. For example, Prison or police station detention center will use antiriot cctv microphone.
   

   mounting position: It is better to mount a CCTV microphone near acoustic source. 

   Connecting mode:

   How to connected to cameras?

1. Audio surveillance microphone can be added to any surveillance system with audio input. The CCTV microphone is typically used as an add-on to CCTV cameras and other types of security cameras that do not have built-in audio.
   
2. This microphone is stand alone as it does not rely on the power source from a security camera. Plug and play cables can be used with these microphones to easily run both the audio and power centrally back to the DVR. Installation of this microphone is very simple for a DIY installer to perform.
   
3. The Mic comes with its own 12V DC power supply and can be used with CCTV Camera Pros stand alone surveillance DVRs or PC based DVRs.
   
4. Because the microphone has a female RCA input and most DVRs have RCA inputs for the microphone inputs, we include two BNC to RCA converters for each end of the plug and play cable. Order the cable with this microphone and the converters are included. See the below audio surveillance connection diagram for more information.
   

1. 3×0.5 RVVP shielded cable transmission distortion.
   
2. ordinary 4 core telephone lines, 
3. five types of network twisted-pair cable
   

1. Automatic Gain Control is an electronic system found in many types of devices.
   
2. Its purpose is to control the gain of a system in order to maintain adequate performance over a range of input signal levels. Or An electronic circuit that tries to keep the video signal at a constant level (1volt peak-peak). Useful on cameras working at low light levels.