I'm trying to remix a song (which I have yet to find) and add a basic drum track and some bass to it. I am basically looking for acoustic versions / covers of popular songs (with no drums), which I will add the drum track to. However in order for this to work, I need to know the tempo, and ideally that tempo has to stay the same for the entire song (or at least it shouldn't fluctuate from verse to verse). Songs recorded in the studio have constant tempo, but covers aren't professionally recorded, so there could be tempo fluctuations. So if my drum track goes steady and the song fluctuates just a bit, it will seem out of sync.
So my question is, is there a way to quickly tell if a song has constant tempo, or will I just have to pull the metronome out and start following the beats? I am using FL Studio for the editing and stuff, if that's any help.