I am working on a new 70's mix which I am trying to record live, not in a DAW. Ive tried to do it 20 times but because the tracks are from the 70's and the tempo is constantly changing it is very VERY difficult. I'm pretty good at riding the pitch but most of the tracks have a relatively short intro, 8-16 bars, which doesn't allow for much time from vocal to vocal. Due to the time changing I can't loop the beginning of the track I am bringing in so ...

I thought there must be a way to "flatten" these tracks or make them so they stay at a specific bpm. How would I do this?

Thanks