Funny, I've been using even primitive text-to-speech on PDFs for years and while nothing compares to an excellent human reader, I find TTS often better than a mediocre human reading. This is mainly because I don't get upset at (and then have to forgive) a machine when it says the "Loovree" instead of the Louvre or in an economic history book pronounces "Keens" for John Maynard Keynes (sound like "Kaynes"). Also the dead neutrality of a machine's reading can jar me less than a numbskull and/or phony human rendition. I must say though that excellent voice actors are to me heaven.