I must advise folks to carefully consider doing any surreptitious recording of conversations with anyone, much less with LEOs.
Federal laws are one thing, but one should first check your State's laws on doing so- lest you find yourself in some serious legal issues above and beyond whatever situation you have gotten into to be recording to begin with.
"The 12 states which definitely require all parties to a conversation to consent before it can be recorded are: California, Connecticut, Delaware, Florida, Illinois, Maryland, Massachusetts, Michigan, Montana, New Hampshire, Pennsylvania and Washington. (In California Law, there is an exception – you can Record an Audio Conversation with the consent of only one party if certain criminal activity (kidnapping, extortion, bribery or a violent felony) is involved. "
Not liking what officer friendly is saying to you about something you know may well attract his attention does not come under "certain criminal activity".
Attempting to have said recording entered as evidence in any court is also going to put the court-and Judge- on notice that you intended to do something you reaonably expected to create legal controversy,and so decided to equip yourself to record the situation in the 1st place..
Tread very carefully on this.