I don't know of any other way than to use Melodyne --

unless there is a RealChart for that RealTrack or
you have a Les Paulverizer or one of its successors. (I guess there are some VST products with that capability. You're probably not alone in the world who wants to create a harmony of an audio track.)

But nevertheless it is not as automatically as it is for midi melodies.


Desktop; i7-2600k, 8 GB mem., Win 10 Pro, BIAB 2017; RB 2017 - latest build
Laptop: i5-2410M, 4 GB mem, Win 10 Pro, BIAB 2017; RB 2017 - latest build