Hi there - I am editing podcasts on Final Cut Pro X - I know there are other options out there, but I am soooooo used to Final Cut that it's just easier. That said, my workflow is to locally record my audio in GarageBand and record the guests with Zencastr or Zoom. When I throw the audio into my timeline, the GarageBand sound slowly starts to drift out of sync. I am recording in 120BPM - not sure if that is correct nor do I know how to change it. Thanks.
Unless Apple has fixed this recently, GarageBand can only record at a 44.1 kHz sample rate. What sample rate are you using to record audio in Zencastr or Zoom? If you're using different sample rates it might account for the drift once you bring all those files into Final Cut; I don't think the bpm in GarageBand is going to make a difference.