You'll need to work your way down to the lowest floor of the lab, and there's quite a bit to handle before getting there. Watch out for Ward Soldiers along the way, and when you spot that electrical field anomaly, maybe take off any artifacts you're wearing to make it easier to pass through. The voice recorder's sitting on a table in the room where you'll face a Bloodsucker - nasty surprise if you're not ready for it. Before you can get to that room though, you'll need to punch in 2605 on the basement door's keypad. Once you find the recorder, you'll hear some interesting stuff between Nestor and Diode that moves the "Answers Come at a Price" quest forward.

Something worth knowing - there's another code, 2603, that you'll need for a metal gate later in this area. The lab's got some decent medical supplies scattered around too, but careful with those anomalies while you're grabbing them. Just remember to stay focused on finding that basement door first, since everything else opens up from there.