I recorded this guy once , and was going to do a little stacking .
His pitching was so good that , each track added would heterodyne and introduce a slow kinda phasing (around 1Hz and below) .
Stumped me for a while as I was after a subtle effect and was not going to "spam" the stack .
I eventually chose words and phrases that I liked from each take and gently made that take the dominant one .
Like I said it was a very gentle thing , and the vocals didn't double so much as transition between each chosen part , with the "lesser" take being in the background .
Also remeber I panned the transitions gnetly too .
Sorry , I was rambling on then !
Ignore me if all that is not important/relevant !