2 - Articulatory and Acoustic Characteristics of Speech Sounds

Abstract

This chapter presents the articulatory and acoustic characteristics of speech sounds. The acoustic characteristics of the speech signal are a consequence of the way the component sounds are produced by the vocal apparatus. The chapter also presents a basic knowledge of the wealth of acoustic information present in the speech signal. It describes the acoustic characteristics of the English phonemes as represented in spectrograms. Various classes of speech sounds have different acoustic patterns as a consequence of the different classes of articulatory gestures required to produce them. Each sound is characterized by several concentrations of energy at various frequency locations. In addition, stop, fricative, and affricate phonemes have energy in many frequency bands as a result of their noise-like sound source. When speech sounds occur in succession, there is a noticeable acoustic transition from one sound to the next as the articulators are in flight between the postures required for each of the individual sounds. The shape and location of this transition is determined by the formants of the two adjacent sounds, which are thought to convey most of the place of articulation information. Although there are articulatory, and thus acoustic, transitions among all contiguous speech sounds, the actual place of articulation of a given sound is altered as a function of sounds that precede or follow it. This phenomenon is called coarticulation and is undirectional or bidirectional.