A perspective on the next challenges for TTS research

The quality of speech synthesis has come a long way since Homer Dudley's "Voder" in 1939. In fact, with the widespread use of unit-selection synthesizers, the naturalness of the synthesized speech is now high enough to pass the Turing test for short utterances, such as voice prompts. Therefore, it seems valid to ask the question "what are the next challenges for TTS research"? This paper tries to identify unsolved issues, the solution of which would greatly enhance the state of the art in TTS.