Acoustic Studies of Voice Variation JYV ASKYLA STUDIES IN COMMUNICATION 7 Pertti Hurme Acoustic Studies of Voice Variation UNIVERSITY OF � JYV ASKYLA JYVAsKYLA 1996 Editor Raimo Salokangas Department of Communication, University of Jyvaskyla Technical editor Kaarina Nieminen Scientific Publishing, University of Jyvaskyla URN:ISBN:978-951-39-8089-4 ISBN 978-951-39-8089-4 (PDF) ISSN 1238-2183 ISBN 951-34-0860-4 ISSN 1238-2183 Copyright© 1996, by University of Jyvaskyla Cover Jorma Luotio Kopi-Jyva Oy and Sisasuomi Oy, Jyvaskyla 1996 ABSTRACT Hurme, Pertti Acoustic Studies of Voice Variation Jyvaskyla: University of Jyvaskyla, 1996, 148 p. (Studies in Communication, ISSN 1238-2183; 7) ISBN 951-34-0860-4 Finnish summary Diss. The present study deals with variation in the human voice. The functions of the voice are addressed and the major practical and theoretical approaches to the voice introduced. A three-fold approach is taken involving phonetics, logopedics and phoniatrics, and singing pedagogy. Voice research is de­ scribed from three perspectives: voice production, acoustics and perception. A central concept is the adduction-abduction continuum, to which various descriptive categories of voice (e.g. creaky and breathy) are related. The study aims at describing the spectral properties of dysphonic voices, of voices varying in vocal intensity, and of supported and covered singing voices. The study also aims at relating the spectral observations to voice production, especially to the adduction-abduction continuum. In addition, the instrumental method used, long-term average spectrum (LTAS) analysis, is evaluated. Four sets of materials were investigated by means of LT AS analysis. Two were spoken materials: dysphonic voices (n = 87) and voices varying in vocal intensity (n = 10); two were sung materials: supported and unsupported voices (n = 8) and coverered and open voices (n = 1). The results indicate that the method used can differentiate between various voices. Several significant differences were observed in dysphonic voices, e.g. voices of patients with paralysis of vocal folds compared to those with laryngeal cancer. The spectra of loud and soft voices differed systematically. There were spectral differences in supported vs. unsupported voices, even though there was much individual and gender-related variation. The LTA spectra of covered and open voices differed systematically. Female and male voices also differed in spectral slope. Even though direct comparison of voices from the four data sets was not possible, the groups which showed distinct spectral differences appeared to form two clusters, "powerless" and "powerful", characterized by steep and shallow spectral slopes, respectively. The study showed LTAS analysis, despite its limitations, to be a useful means of investigation into the human voice and its variation. Keywords: voice variation, dysphonia, vocal intensity, supported voice, covered voice, gender, long-term average spectrum analysis CONTENTS PREFACE 1 INTRODUCTION 9 .2 VOICE AND VOICE VARIATION 11 2.1 Definition of voice 11 2.2 Evolution and ethology of the human voice 13 2.3 Functions of voice 14 2.4 Approaches to voice 17 2.4.1 Phonetic tradition 17 2.4.2 Phoniatric-logopedic tradition 21 2.4.3 Singing pedagogy and singing research 22 tradition 2.5 Study of voice 23 2.5.1 Historical notes 23 2.5.2 Production 24 2.5.3 Perception 32 2.5.4 Acoustics 32 3 VOICE ACOUSTICS 36 3.1 Long-term spectrum analysis 36 3.2 Spectral correlates of voice 41 3.2.1 Dysphonic voice 41 3.2.2 Vocal intensity 44 3.2.3 Voice types in singing 45 3.2.4 Female and male voice 48 4 PROCEDURE 52 4.1 Research questions 52 4.2 Material 53 4.2.1 Dysphonia 53 4.2.2 Vocal intensity 55 4.2.3 Supported and unsupported singing 56 4.2.4 Covered and open singing 57 4.3 Methods 58 4.3.1 Speaking voice 58 4.3.2 Singing voice 61 4.4 Statistical treatment and summary of material 64 and methods 5 RESULTS 65 5.1 Dysphonia 65 5.1.1 Spectral levels at nine frequencies 65 5.1.2 Spectral levels in three frequency areas 68 5.1.3 Spectral levels of the lowest two harmonics 69 5.1.4 Further comparisons 70 5.1.5 Synopsis of the results on dysphonia 72 5.2 Vocal intensity 74 5.2.1 Spectral levels at nine frequencies 74 5.2.2 Spectral levels in three frequency areas 75 5.2.3 Spectral levels of the lowest harmonics 76 5.2.4 Synopsis of the results on vocal intensity 80 5.3 Support in singing voice 83 5.3.1 Acoustic measurements 83 5.3.2 Acoustic measurements and perceptual 95 evaluation 5.3.3 Synopsis of the results on support 100 5.4. Covered and open singing voice 102 5.4.1 Amplitude levels and the voice types 102 5.4.2 Spectral levels of the lowest two harmonics 105 5.4.3 Harmonics with maximum levels 107 5.4.4 Synopsis of the results on covering 108 6 DISCUSSION 109 6.1 Spectral differences in the speaking and singing voice 109 6.1.1 Overview 109 6.1.2 Normal and dysphonic voice 113 6.1.3 Vocal intensity 114 6.1.4 Support in the singing voice 115 6.1.5 Covering in the singing voice 116 6.1.6 Female and male voice 118 6.2 Evaluation of the study 121 6.3 Future directions 124 YHTEENVETO 127 BIBLIOGRAPHY 132 APPENDIX 147 PREFACE The human voice is an enchanting object of study. It shows much variation, both within and between individuals. It can be investigated on many levels: as physiological and biomechanical activity, as an acoustic signal, and in the process of perception and interpretation in a social context. This study concentrates on the acoustic aspects of voice variation. The roots of this study go back to the seminal work of Professor Kalevi Wiik at the University of Turku. I am grateful to him for introducing me to the fascinating world of phonetics and linguistics and also for providing me with the incentive to find my own path in the academic world. The path led to the University of Jyvaskyla, where interdisciplinary research on voice started in the late 1970s. Collaboration with Professor Aatto Sonninen, the Grand Old Man of Finnish phoniatrics, has greatly widened my views about the human voice. I warmly thank him for the many scientific discussions and vigorous arguments we have had and continue to have while carrying out research and writing reports on various aspects of the human voice. I also thank Professor Jaakko Lehtonen for providing the impetus for my early studies of the human voice using long-term average spectrum analysis and for encouragement during the process leading to the completion of this dissertation. I am grateful to the reviewers of the manuscript for this dissertation, Docent Britta Hammarberg and Professor Erkki Vilkman, for their insight­ ful comments and suggestions that were useful in writing the final version. My research activities have brought me into professional contact with many voice and speech researchers both in Finland and abroad. I have had the opportunity to spend shorter or longer study periods e.g. in Sweden, the United States, Italy and Russia. I wish to thank colleagues and friends, wherever they are, for the many fruitful discussions on a variety of topics related to the theme of this work. I also thank the staff and students at the Department of Communication where I work: I appreciate the open and future-oriented atmosphere which prevails at the department. The financial support given me by the University of Jyvaskyla and the Faculty of Humanities has made it possible for me to concentrate on writing this dissertation free from my teaching obligations during two semesters. I thank the university for accepting this work in the Studies in Communication series and for g1vmg me a grant toward the printing expenses. I also thank Professor Raimo Salokangas, the editor of Studies in Communication, and Kaarina Nieminen, the Secretary of Scientific Publishing, for their friendly co-operation. Thanks are also due to Graphical Designer Jorma Luotio for translating my ideas about the cover page into an artistic design and to Senior Lecturer Michael Freeman for professional help in revising my English. My deepest thanks go to Maarit Valo, my colleague and my wife, for her unfailing support and encouragement. I particularly value our discus­ sions, often at the kitchen table, on the human voice, communication and research. I dedicate this work to my parents, Irma and Viekka, and to the next generation, Freija and Rauli. Research is the outcome both of experience and of experimentation. Jyvaskyla, November 1996 Pertti Hurme 1 INTRODUCTION Human beings are skilful in modifying and coloring their voice to express themselves. Such modification can be temporary, as in expressing joy or fear. It can also be more permanent, as when adopted to indicate member­ ship in a group. This capacity for variation in voice has been recognized by scientists for a long time. For instance, Aristotle reflected extensively on the subject. In On things heard (quoted in Barnes, 1984) he wrote: "It is the quickness of breathing which makes the voice shrill, force which makes it hard. So it happens that the same individuals have not only sometimes a shriller and at other times a deeper voice, but also at times a harder and at times a softer voice." Aristotle was observing variation in a person's voice. According to him, the reasons for this variation are quickness of breathing and force. Quickness of breathing may refer to a relatively high air-flow through the glottis during voice production (phonation).