So, over the last two days, I had two friends run into the same problem while editing DSLR footage in FCP. The problem was that even though the sequence settings matched up with the footage from the DSLR,the audio that was recorded separately was mysteriously drifting out of sync. This is a very frustrating problem that I personally lost quite a few hours over. I tried literally everything I could think of. I thought it was the recorder I was using, my sequence settings, etc. I literally checked everything that logically would make sense. To no avail. That’s because the solution defies logic. For some inane reason unknown to mankind FCP ships with a weird “quirk”. Even though when editing DSLR footage there is no “capture” happening, the Capture Settings have to match your footage/sequence settings or you can get Audio that drifts out of sync, Hope that saves you some headaches and helps you get back to editing.
What I am referring to here is that the frame rate in your Capture Settings, not Log and Transfer, needs to match the frame rate of your footage and your Sequence Settings.