I'm pretty sure that the "weird sound" we hear are the reverberation early reflections. Reverb processor introduces a slightly delayed and damped set of reflections (10 to 250 ms late), so what we hear is the first note attack, slightly lower than the sustained note (the singer starts a bit low and corrects herself along), that gives that effect.
I've been a sound engineer until 1996, and I know that auto-tune definitely use some formant-aware phase shifting, so that a slight pitch correction (up to a couple of commas) must be essentially inaudible if properly used. Heck, back in the 1980s when we only had Eventide H3000 to save a poor performance, we could make a convincing approximation of the auto-tune effect in post-production, and when the digitech vocalist MV-5 became available, it made a really decent job at real-time pitch-correction, and it was back in 1995. Do you really think that a state-of-the-art fx module used by a competent sound engineer in 2010 would be audible? No way, sir.
I've been a sound engineer until 1996, and I know that auto-tune definitely use some formant-aware phase shifting, so that a slight pitch correction (up to a couple of commas) must be essentially inaudible if properly used. Heck, back in the 1980s when we only had Eventide H3000 to save a poor performance, we could make a convincing approximation of the auto-tune effect in post-production, and when the digitech vocalist MV-5 became available, it made a really decent job at real-time pitch-correction, and it was back in 1995. Do you really think that a state-of-the-art fx module used by a competent sound engineer in 2010 would be audible? No way, sir.