1.1.1. Source-Filter Model

Speech, the acoustic manifestation of language, is probably the main means of communication between human beings. The invention of telecommunications and the development of digital information processing have therefore entailed vast amounts of research aimed at understanding the mechanisms of speech communication.

Speech can be approached from different angles. In this chapter, we will consider speech as a signal, a one-dimensional function, which depends on the time variable (as in [BOI 87, OPP 89, PAR 86, RAB 75, RAB 77]). The acoustic speech signal is obtained at a given point in space by a sensor (microphone) and converted into electrical values. These values are denoted s( t) and they represent a real-valued function of real variable t, analogous to the variation of the acoustic pressure. Even if the acoustic form of the speech signal is the most widespread (it is the only signal transmitted over the telephone), other types of analysis also exist, based on alternative physiological signals (for instance, the electroglottographic signal, the palatographic signal, the airflow), or related to other modalities (for example, the image of the face or the gestures of the articulators). The field of speech analysis covers the set of methods aiming at the extraction of information on and from this signal, in various applications, such as:

• speech coding: the compression of information carried by the acoustic signal, in order to save data storage or to reduce transmission rate;

• speech recognition and...