Basically I suspect that someone I know is spreading malicious rumors about me, which I think falls under defamation. I've thought about trying to talk with them and find the answer, but if they do admit to it, I have nothing to go with but hearsay, so I thought about recording the convo without their knowledge. While trying to find an answer I've found mixed results. Some sources says under no circumstances, some say if a crime is being committed, and one says if it's within a public domain. Also if there is a good resource to find legal answers for local, state, and federal laws i'ld definitely appreciate it.
I don't know much about Maryland's law specifically, but this question frequently comes up in the context of newsgathering.
To that end, the Reporter's Committee for Freedom of the Press has a pretty helpful Reporters' Recording Guide, which will walk you through the differences in the law from state to state, much of which would probably be informative for your purposes, as well. You can also just jump straight to the recording laws in Maryland.
Wiretapping laws are no joke, though, so you should consult a lawyer before proceeding.
So for the purposes of what you're asking, Oral Conversation does not count as electronic conversation (basically, if you call on the phone, it's electronic. If you're chatting with him in person, it's oral). Thus, the capture of Audio by a recording device relies on "reasonable expectation of privacy" which is circumstantial. If you are in a public place (not a bathroom, changing room, or similar) where another party could hear the conversation has no reasonable expectation to privacy. Thus if you could get this person in a publicly accessible area, it could be legal.
This article cites several case laws that further clarify the matter and was written by a practicing MD Lawyer and cites MD case law. As the disclaimer on the bottom notes, it's probably best to consult a lawyer before you carry out your recording just to be sure. Many offices do consultations for free.