This is my daily bread-and-butter, so I feel qualified to comment.
It is a common misconception that it sounds natural to change tempo gradually. In fact, it
sounds better and is more natural if done cleanly. There are of course bands that always
start a song slow and speed up throughout the song - that's a different problem.
Example #1: Exactly as you say. Set the tempo changes in jumps, not smooth transisions.
If the band has difficulty following, try the average tempo throughout, then in post, cut the
track into its sections and set the tempo changes. Ctrl+stretch each section as needed.
Example #2: Been there, done that. If they cannot even keep time with each other, you have a big job on your hands.
If the guitarist/vox is moving ahead and then behind the beat in a musical way ("Diva Mode" is what I call it for want of a better term), then it is part of the musical expression and you must try convince the drummer to keep a steady beat for the "Diva" to work with.
But if it's just lack of ability, then you have your work cut out. Let the scratch vox do his best, then send the band to a coffee break whilst you cut up the performance into roughly stable subsections and shrink-stretch the clips to fit the timing grid.
Note: There is a bug currently being fixed. If you Ctrl+stretch/shrink a clip, the Clip/Snap Offset value changes from "0" to some random value. This frustrates subsequent snap-to-grid attempts. You may need to manually set them to "0" again.
post edited by jpetersen - 2016/01/02 18:16:29