Speech synthesis and emotions: a compromise between flexibility and believability

The synthesis of emotional speech is still an open question. The principal issue is how to introduce expressivity without compromising the naturalness of the synthetic speech provided by the state-of-the-art technology. In this paper two concatenative synthesis systems are described and some approaches to address this topic are proposed. For example, considering the intrinsic expressivity of certain speech acts, by exploiting the correlation between affective states and communicative functions, has proven an effective solution. This implies a different approach in the design of the speech databases as well as in the labelling and selection of the “expressive” units. In fact, beyond phonetic and prosodic criteria, linguistic and pragmatic aspects should also be considered. The management of units of different type (neutral vs expressive) is also an important issue.