We have discussed the sounds of speech in terms of articulatory and acoustic data and in terms of theoretical models of speech. In this last chapter, we present some of the acoustic correlates of various speech sounds of English. This review will not be a comprehensive study of the acoustic correlates of the sounds of human speech or even of the sounds of English, but it should be a useful starting point for more detailed study.

One of the challenges of speech research is to determine what aspects of the acoustic signal are relevant to the listener for perceiving the sounds of speech. As is apparent from the earlier discussions on the acoustics of speech, the speech signal is complex with temporal, durational and spectral variations. However, research has shown that listeners can perceive speech with a greatly “stripped down” version of the acoustic signal. In other words, only certain aspects of the acoustic signal seem to be relevant to the listener for perceiving the phonetic dimensions of speech. These relevant attributes for speech are called acoustic correlates or acoustic cues. Let us review some of the acoustic cues necessary for the perception of English speech sounds.

Vowels

The frequency positions of the first three formants are sufficient cues for listeners to identify the vowels of English. The formant frequency relations that specify the vowels of English are inherently relational rather than absolute since different-sized supralaryngeal vocal tracts will produce different absolute formant frequencies.