One of the most difficult problems in speech to date is prosodic modeling. But there is also room for improvement in both melodic and durational models. In natural speech the prosodic parameters interact in a way that is still unknown, in order to supply the listener with prosodic information while keeping the feeling of fluentness. Understanding the interplay of these parameters is today one of the hottest topics for research on speech synthesis. The last step for speech output is synthesis of the waveform, according to the segmental and prosodic parameters defined at earlier stages of processing.
Typical parameters are the position and kinematics of articulators.
Then the sound radiated at the mouth is computed according to equations of physics. 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 .