1 - Pitch in Humans and Machines

Summary

Introduction

In this first chapter, some phonetic information is given which will be required for an active engagement in research in the area of tone and intonation. For further information on the articulatory, acoustic, and technological facts, handbooks like Laver (1990), Ladefoged (1996), Johnson (1997), Rietveld and van Heuven (1997), Reetz (1999) should be consulted.

Frequency of vocal fold vibration, fundamental frequency (F₀), and pitch

Pitch is the auditory sensation of tonal height. We have this sensation when listening to the difference between [s] and [∫], for instance, but in speech, it is most precise when it reflects the periodicity in the acoustic signal. Periodicity amounts to repetitions of the same pattern of vibration, each such repetition being a period and corresponds to a closing-and-opening action of the vibrating vocal folds. The actual shape of the speech signal during a period determines the sound quality (the vowel quality, say) that we perceive. In panel (a) of figure 1.1, 25 milliseconds (ms) from the speech waveform produced by a woman are shown. During that time, just over six periods were produced, representing as many vibratory cycles of the vocal folds. These are two muscles, situated halfway down the larynx, which run front to back from the inside of the thyroid (the shield cartilage sticking out in the front of the neck) to the two arytenoids, which are located above the cricoid. In a relaxed state, there tends to be a slit between the vocal folds, known as the glottis, through which we breathe.