This type of synthesizer is rather far from applications and marketing because of its cost in terms of computation and the underlying theoretical and practical problems still unsolved. The filter, described by a small set of formants , represents articulation in speech. It models speech spectra that are representative of the position and movements of articulators. The source represents phonation . It models the glottal flow or noise excitation signals .
Concatenative synthesis is based on speech signal processing of natural speech databases.
The segmental database is built to reflect the major phonological features of a language. Several high-quality concatenative synthesizers, including multilingual systems , are marketed today. When one works on phonetic rule definition or segment concatenation, a robust and quick assessment methodology is absolutely necessary to improve the system. Besides, it is also necessary in order to compare the systems to each other. As far as speech naturalness is concerned the problem is still almost untouched.