What is the best free AI voice synthesis program out there?

What I'm looking for is a program that can take raw voice clips (\~10 minutes of actual mp3 recording) and create a synthesised voice from that. I ask because I want to make some custom voices of fictional characters, bit like what [15.ai](https://15.ai) does

I've had experience working with AI programs so something on GitHub as long as it's not too much of a pain to setup is fine as well

ai artificial free voice