Is there any real-time text-to-speech software?
Dragon Naturally Speaking v6 may be an option. Trial available here. Have used with school and it performed well in loud environments as well as those that are quiet. Doesn't need an internet connection after downloaded, so is a very good idea. Also, the macOS built in dictation software may be downloaded for free, but is not as reliable. 

For more, see this thread, which says 


  eSpeak is a brilliant opensource text to speech project. It's the default TTS software on many Linux distributations, but there's a Mac version available and it works great. There is also a project based on eSpeak called Mbrola which adds "singing" functionality.