Line-in interface takes Titathink camera to monitor sound with an external sound pickup device (Microphone). Some users need the some of Titathink cameras that didn’t built-in microphone module to monitor sound, user can use this line-in interface.

The specification of Line-in interface:
It is female RCA jack that requires male RCA or BNC connector.

The specification of external sound pickup device (Microphone):
Titathink camera can work with most of CCTV sound monitoring devices.
The specifications of audio for camera line-in interface is as follows:

RCA connector.
Frequency range: 100-100 KHZ.
Input impedance: 600 ohm non equilibrium.

Also you can learn more about the connectors by refering to below article :
https://support.titathink.com/knowledge-base/what-kind-of-sound-pick-up-device-should-i-purchase

If your microphone or sound pickup device is not working, please take a try:
https://support.titathink.com/knowledge-base/the-sound-pick-up-device-works-with-tt520pw-unsuccessfully