I haven’t used autotune much until now, and only used the free ReaTune VST that comes for free with Reaper.
As far as I can see, only single notes can be easily pitch corrected. Are there any VSTs that can automatically tune harmonized lines or even full chords?
I think Melodyne might be able to do this, it’s the most advanced pitch correction software, as far as i know.
Awesome thank you! I am kind of curious from a sorta mathematical point of view 
Lots of FFTs needed for that I would think.
The This is Pop series on Netflix has an episode about auto-tune and they interview the creator, Dr. Andy Hildebrand, who designed the software with help from his background in geophysics and he stresses the effect was never supposed to be audible and used the way Cher and everyone afterwards used it. 
Never give musicians something designed to be used one way it will invariably be used in a completely different way.
Read this a while ago when it came out. They don’t really get into enough detail for me (very little ML background) to get anything valuable from it, but was a good read. I believe most purely math/algorithm methods have been sort of meh at best.
My pitch correction rant…
I have no problems with people using it. A good musician is gonna sound live. Artists who rely on it will be exposed at their live performances and have a shorter career So if people need to use it on good singers to save time and keep costs down, or better yet, keep a take that had some magical quality that the singer might not easily be able to reproduce (but was a tiny bit “pitchy”)…fine. I can live with that just like I can live with people punching in spots of guitar solo for similar reason.
What bugs me to no end is when I can hear pitch correction used in genres where it’s not supposed to be audible, on singers who really don’t need it (e.g. Adele, Keith Urban, Ed Sheeran, Christina Aguilera et al). When this happens, it’s extremely lazy audio engineering. I’ve never used the actual “auto tune” product but I’ve used Melodyne extensively, as well as what my version of Cubase had out of the box (VariAudio). The tweaks I did were never audible, because I was very surgical with the tools. This makes me believe that industry professionals are just using extreme pitch quantization on the little part of the take that was out, instead of keeping it musical by chopping the note up and smoothly addressing the issue.
end of rant and thread derail…
I’ve always wondered if “tuning chords” was possible too, and if so if there are adverse artifacts that expose what’s going on, equivalent to the “Cher” effect on single lines. Technology and AI are really making strides. I’m sure it’s just a matter of time before all this stuff gets flawless and allows musicians and engineers to be even lazier yet lol!
Oh yes, it’s definitely possible - Melodyne’s more advanced versions offer this. Melodyne and products like it are everywhere - but that’s okay - they will be replaced and made redundant by the hordes of synthesized voice modules offering AI vocals and AI instruments of every kind. Heck, you don’t need to do much these days - just button mash and you have a song! Maybe a pretty good one, too!