A deliberately gentle, non-technical introduction to the topic. Every item in the small and carefully-chosen bibliography is worth following up.
Simon King “An introduction to statistical parametric speech synthesis” in Sadhana, Volume 36, Issue 5, October 2011, pp 837–852
Author’s version with the original title “A beginners’ guide to statistical parametric speech synthesis” – this is the preferred version
Publisher’s version (with their modification of the title and other unnecessary edits)