Unsurprisingly The Voice is extensively planned, even down to what the judges ask the contestants while they're on stage. Per the Woman's Day insider, the judges "will often get a name or a back story to make sure they're asking the right questions."
@Rockitlikearedhed also mentions this in the Reddit thread, revealing that the blind auditions are recorded weeks before the actual show and that "you have to pretend it's on the day itself."
In terms of picking a song, it's apparent that the contestants don't have a lot of choice. "My friend was on the UK version last year and he said for each round they let him choose one of three songs, or sometimes they just gave him a song," user @amkamins wrote.
Essentially, there's a lot the production team behind The Voice don't want you to know — and for good reason. If there weren't surprises and some drama along the way, why would you tune in?