While I have never used Autotune in Reaper, I know that pitch correction can be adjusted to have a PROFOUND effect on the sound of a track. I record a one-man quartet; and on one hymn I did a few months ago, I set my pitch correction to its maximum value. The result was very solid tuning of all four parts - a sound unlike anything I have heard before! In some ways, I like the sound; yet I know that it would be rather extreme if I were to use pitch correction set that tightly on all of my quartet recordings. Still, I admire that performance as in a way the epitome of one of my goals of the quartet which I call "Crystal Control." That particular aspect of what I am after is to create a vocal tone as if the pitches were controlled or keyed from an electronic keyboard. My college voice teacher would run me out of town if she heard that performance, and I would agree that I wouldn't want that on many of the songs I record; but at times I like it. Yes, I have no doubt that a good pitch-correction routine can DEFINITELY make a difference between the corrected and uncorrected sound. In the extreme maximum settting, a singer with even a moderately wide vibrato might produce something which could sound something like a trill. I suspect that you will notice a difference if you find the settings needed to get it. Of course, if you happen to sing with a very straight tone as I do and you sing extremely well in tune, maybe the pitch correction doesn't need to do much to your voice. The phase difference you notice might be occurring due to a slight time delay introduced by the correction function.