I recorded a choir using ORTF mic set -up, with an additional stereo mic behind those mics. On mixdown, panned the ORTF mics slightly left and right and kept stereo mic centred. Some tuning was off, so used Melodyne to correct. In just a couple of spots where I'd corrected the tuning, on listening to the mix there seems to be some kind of weird shift in the stereo image. Not evident when each track is solo'd - just when all three playing together. I deduced it must be phase problems introduced by the tuning corrections. I tried inverting the phase on those spots; tried time-shifting one of the tracks by a few ticks, but the problem persists.
Then I inserted Logic Pitch Shift on one of tracks, and strangely, if I leave the Pitch at 0 (not even 1 cent of adjustment), the problem disappears. However, there is an audible difference in the nature of the sound on that track.
Can anyone help me with:
1) What is the Pitch Shift plugin doing to the sound even when not set to alter the pitch at all? Although it fixes the phasey problem, I don't want to use it if it is messing with other aspects of the mix.
2) Any ideas on whether I'm correct about phase being the issue on those retuned spots where the stereo image shifts, and how to fix that?