>>272514565
https://github.com/auspicious3000/autovc has a demo page as well. Pretty convincing but not transparent to my ears.

>>272514732
You can look into black box optimization. It'd still take a lot of work to define an objective function though; I don't even know where to start for that, other than having humans give subjective opinion from one setting to the other. Then you've got a croudsourcing problem.