Using Michrophone with RLN-36

Ed

I have a customer who needs microphone access to his cameras via his RLN-36 unit. I've contacted support and they've sent me documentation but the port on the NVR is an "Audio-In" port. Documentation states that this is a microphone port. It's an RCA jack and in my experience, microphones normally don't use RCA jacks. RCA would be used for an audio line-level input. Has anyone connected a microphone to an RLN-36? Is it a straight connection or do I need a preamp to bring the mic level to a line level for audio input?