The Acoustics of Nasalized Speech

Abstract

In his classic book, The Science of Musical Sounds, Dayton C. Miller (12) began his chapter on " Physical Characteristics of Vowels " with the following statement: " The vowels have been more extensively investigated than any other subject connected with speech ". If Miller could make that statement, some 45 years ago, what might be said today? In the 1960s we look on his work as that of a pioneer, probing into a whole new era of acoustic investigation of speech. Even so, almost half a century later, there remain many unanswered questions. The acoustic study of nasalized speech has a much shorter history than the study of vowels, and a correspondingly more limited literature. There have nevertheless been a number of attempts to search out and to describe the characteristic changes in the acoustic signals of speech, especially vowels, that result when speech is nasalized. A detailed review of these studies is outside the scope of the present discussion. However, one generalization that can be made from the acoustic studies of na-salization is of central interest; that is, that the data do not provide the basis for a simple, unequivocal, and definitive description of the acoustical effects of nasalization. On the contrary, variability and inconsistency ap— pear to be the rule. The results reported by one investigator are frequently not corroborated by the data from another study, and the changes in the acoustic signal that appear to characterize nasal resonance under one set of conditions cannot be found for other subjects or for a different sample of speech. Thus, Dickson (3) stated that his study ". .. emphasizes the variability in the acoustic characteristics of nasality from person to per— son " and he adds that " It would seem that nasality can be specified in many ways depending upon the specific configurations of the oral, pharyn-geal and nasal cavities " .