Why so different? Aspects of voice characteristics in operatic and musical theatre singing EVA BJÖRKNER - PDF

Why so different? Aspects of voice characteristics in operatic and musical theatre singing EVA BJÖRKNER Doctoral Thesis Stockholm, Sweden 2006 TRITA CSC A 2006:23 ISSN ISRN KTH/CSC/A 06/23 SE

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Why so different? Aspects of voice characteristics in operatic and musical theatre singing EVA BJÖRKNER Doctoral Thesis Stockholm, Sweden 2006 TRITA CSC A 2006:23 ISSN ISRN KTH/CSC/A 06/23 SE ISBN ISBN KTH School of Computer Science and Communication SE Stockholm Sweden Akademisk avhandling som med tillstånd av Kungl Tekniska högskolan framlägges till offentlig granskning för avläggande av filosofie doktorsexamen fredagen den 8 december kl i sal F3 Lindstedtsvägen 26, Kungliga Tekniska högskolan, Stockholm. Eva Björkner, december 2006 Tryck: Universitetsservice US-AB Abstract This thesis addresses aspects of voice characteristics in operatic and musical theatre singing. The common aim of the studies was to identify respiratory, phonatory and resonatory characteristics accounting for salient voice timbre differences between singing styles. The velopharyngeal opening (VPO) was analyzed in professional operatic singers, using nasofiberscopy. Differing shapes of VPOs suggested that singers may use a VPO to fine tune the vocal tract resonance characteristics and hence voice timbre. A listening test revealed no correlation between rated nasal quality and the presence of a VPO. The voice quality referred to as throaty, a term sometimes used for characterizing speech and non classical vocalists, was examined with respect to subglottal pressure (Psub) and formant frequencies. Vocal tract shapes were determined by magnetic resonance imaging. The throaty versions of four vowels showed a typical narrowing of the pharynx. Throatiness was characterized by increased first formant frequency and lowering of higher formants. Also, voice source parameter analyses suggested a hyperfunctional voice production. Female musical theatre singers typically use two vocal registers (chest and head). Voice source parameters, including closed quotient, peak to peak pulse amplitude, maximum flow declination rate, and normalized amplitude quotient (NAQ), were analyzed at ten equally spaced subglottal pressures representing a wide range of vocal loudness. Chest register showed higher values in all glottal parameters except for NAQ. Operatic baritone singer voices were analyzed in order to explore the informative power of the amplitude quotient (AQ), and its normalized version NAQ, suggested to reflect glottal adduction. Differences in NAQ were found between fundamental frequency values while AQ was basically unaffected. Voice timbre differs between musical theatre and operatic singers. Measurements of voice source parameters as functions of subglottal pressure, covering a wide range of vocal loudness, showed that both groups varied Psub systematically. The musical theatre singers used somewhat higher pressures, produced higher sound pressure levels, and did not show the opera singers characteristic clustering of higher formants. Musical theatre and operatic singers show highly controlled and consistent behaviors, characteristic for each style. A common feature is the precise control of subglottal pressure, while laryngeal and vocal tract conditions differ between singing styles. In addition, opera singers tend to sing with a stronger voice source fundamental than musical theatre singers. Key words: operatic singing, musical theatre singing, voice source, subglottal pressure, flow glottogram, inverse filtering, formant frequencies, amplitude quotient (AQ), normalized amplitude quotient (NAQ), vocal registers, velum opening, throaty voice. Contents Contents 1 Abbreviations 2 List of publications 3 Author s contribution to the papers 4 Introduction 5 Respiration 5 Subglottal pressure 6 Larynx and phonation 7 Cartilages Vocal folds Voice source Formants and articulation 10 Source vocal tract interaction 11 Vocal registers 11 Spectral balance 12 Variation of vocal loudness 13 Methods for voice analysis 14 Flow glottogram parameters Electroglottography Magnetic resonance imaging Singing versus speech 18 Singing versus singing different singing styles 18 Purpose of the studies 21 Overview of the studies 23 General discussion 41 Conclusions 43 Acknowledgements 44 References 46 Papers A E 1 Abbrevations AQ DEGG dpeak EGG F0 F1 Fn H1 H2 MFDR MRI NAQ Up t p Psub Psen Qclosed SPL T0 Tcl VPO amplitude quotient (Up t p/ MFDR) differentiated EGG signal peak derivative of the glottal flow (=MFDR) electroglottography fundamental frequency first formant frequency n:th formant frequency level difference between first the two partials in voice source spectrum maximum flow declination rate magnetic resonance imaging normalized amplitude quotient (AQ/T0) glottal peak to peak flow amplitude subglottal pressure normalized excess pressure closed quotient (ratio glottal closed phase time to period time) sound pressure level period time closed phase time velopharyngeal opening 2 List of publications This thesis is based on the following papers, referred to by letters A through E. Paper A Velum Behavior in Professional Classic Operatic Singing. Peer Birch, Bodil Gümoes, Hanne Stavad, Svend Prytz, Eva Björkner & Johan Sundberg. Journal of Voice, 2002; 16 (1): Paper B Throaty Voice Quality: Subglottal Pressure, Voice Source, and Formant Characteristics. Anne Maria Laukkanen, Eva Björkner & Johan Sundberg. Journal of Voice, 2005; 20 (1): Paper C Voice Source Differences between Registers in Female Musical Theatre Singers. Eva Björkner, Johan Sundberg, Tom Cleveland & Ed Stone. Journal of Voice, 2006; 20 (2): Paper D Subglottal Pressure and Normalized Amplitude Quotient Variation in Classically Trained Baritone Singers. Eva Björkner, Johan Sundberg & Paavo Alku. Logopedics Phoniatrics Vocology. In Press, Available online October Paper E Musical Theatre and Opera Singing why so different? A study of Subglottal Pressure, Voice Source and Formant Frequency Characteristics. Eva Björkner Journal of Voice. Submitted Other related papers by the author Comparison of Two Inverse Filtering Methods in Parameterization of The Glottal Closing Phase Characteristics in Different Phonation Types. Laura Lehto, Matti Airas, Eva Björkner, Johan Sundberg & Paavo Alku. Journal of Voice. In Press, Available online 14 February 2006 An Amplitude Quotient Based Method to Analyze Changes in the Shape of the Glottal Pulse in the Regulation of Vocal Intensity. Paavo Alku, Matti Airas, Eva Björkner & Johan Sundberg J. Acoust. Soc. Am. 2006; 120(2); Author s contribution to the papers Paper A Author EB performed all measurements, assisted during the recordings, and prepared the analysis. Coauthors JS, PB, HS, and BG planned the investigation. Co author JS assumed the main responsibility for writing the report. Paper B Author EB carried out the major part of the MRI analysis, of the acoustic measurements, and of the analyses (area functions, flow glottogram characteristics, formant frequencies). The investigation was planned and the recordings were carried out by coauthors AML and JS. The manuscript was jointly authored by coauthors EB, JS and AML. Paper C The major part of the work (analysis and writing) was carried out by the author EB. Coauthor JS assisted in the analysis and in writing the manuscript. The investigation was planned and the recordings were made by co authors TC, ES and JS. Paper D The major part of the work (analysis and writing) was carried out by the author EB. Coauthor JS assisted in editing the manuscript. The recordings were made for another study under the supervision of JS. Paper E This work was designed and carried out entirely by the author EB. JS assisted in editing the manuscript. 4 Introduction The voice is the major tool in speech communication. Also, it is possibly the most flexible among musical instruments. The singing voice is unique in the sense that we can not only produce a wide range of pitches and voice qualities with it, but also add words to elucidate and complement our musical expression. Phonation is produced when air expelled from the lungs causes the vocal folds to vibrate. These vibrations generate a pulsating airflow which constitutes an audible source of acoustic energy, i.e., sound. This source sound is controlled by the degree of constriction of the vocal folds, the subglottal pressure, the volume of the airflow, and is modified in the vocal tract. Typically, voiced sounds are all the vowels as well as many consonants. In spoken languages, for example in English, approximately 78% of the phonemes are voiced (Catford 1977). In singing this figure is considerably higher. To produce voiced sounds, three basic systems are involved; the respiratory system, the voice source, and articulation. The respiratory system is a compressor like system, controlling breathing and phonation. When speaking habitually, the elastic and muscular forces involved act at an unconscious level but as vocalizing becomes an art, like in stage speech or singing, the control of the respiratory muscles needs to be precise, and hence conscious and trained. The voice source is the pulsating transglottal airflow produced by the vibrating vocal folds. When the combination of subglottal pressure and glottal configuration are appropriate the vocal folds start to oscillate and sound is produced. The sound varies in terms of quality and frequency depending on the muscular and aerodynamic conditions in the larynx. The adjustment of the articulators, i.e., the pharynx, the tongue, the jaw opening, the soft palate, and the lips, changes the acoustic conditions in the vocal tract. These conditions in turn influence the spectral properties such that the sounds produced can be perceived and interpreted in terms of speech sounds and voice qualities. This introduction will present descriptions of the anatomy and function of the voice organ, voice source analysis methods, differences between speech and singing, and will consider aspects of the key question of this thesis, the differences between singing styles. Respiration Respiration is the act of breathing. The respiratory apparatus consists of (a) an upper cavity, i.e., the thorax, formed by the rib cage and the pulmonary system, (b) a lower cavity, formed by the abdomen, and (c) the diaphragm, that separates these two cavities. The lungs are located and suspended in the rib cage and respiratory events primarily result from modification of the rib cage dimensions. Chest wall movements are influenced by both active muscle forces and passive forces. The passive forces originate from (a) elastic recoil in the rib cage, (b) resistance to airflow by the airways, (c) gravity, and (d) from the inertial properties of the respiratory system (Rodarte & Rehder 1986). Air enters the body through the upper airways; the nose, the mouth, the pharynx (the 5 throat), and travels down through the larynx (see section Larynx and phonation) and the trachea (the windpipe) into the lungs. During inspiration, an active contraction of the external intercostal muscles lifts the ribs and pulls them upward and outward and the diaphragm (the most important inhalatory muscle) lowers the floor in the thorax. These actions increase lung volume and create a pressure drop in the lungs, allowing air to rush in through the open airways. In singing, but also in phonation in general, voluntary control of both inhalatory and exhalatory muscles is of paramount importance. In quiet expiration, by contrast, the inhalatory muscles automatically relax and the thorax unit recoils back to its resting position. Vital capacity is crucial to a singer s maximum phrase duration; it is the amount of air in the lungs that can be expelled after maximum inhalation. Non singers and country singers have been found to use only slightly higher lung volumes than those used by speakers (Hixon et al. 1973; Hoit et al. 1996; Cleveland et al. 1997). Professional operatic singers, on the other hand, use notably higher portions of their vital capacity. Also, possible gender differences have been revealed; female operatic singers were found mostly to spend between % of their vital capacity in a phrase while male singers spend only % (Thomasson & Sundberg 1997). In addition, high lung volumes are associated with glottal abduction forces (Iwarsson et al. 1998). Subglottal pressure The subglottal pressure (Psub), produced by the respiration system, is the pressure below the closed or the semi closed glottis. Psub is one of the main factors for vocal fold vibration and the primary factor contributing to vocal loudness (Gauffin & Sundberg 1989). Increasing Psub in terms of increasing vocal loudness generally tends to raise fundamental frequency (F0) in speakers (Gramming 1988). In addition, the control of Psub has been found to be less precise when male operatic singers applied a non habitual inhalatory pattern (similar to that found in non singers) rather than a habitual pattern (Thomasson 2003). Direct determination of Psub is a tricky and invasive procedure due to the need to reach a measurement position below the adducted vocal folds. An alternative technique to measuring Psub in phonation (indirect and non invasive) is to capture the intra oral pressure during the occlusion for the consonant /p/. This can be done by inserting a tube connected to a pressure transducer, into the mouth. Data derived from such measurements are often also referred to as Psub. To initiate vocal fold vibration Psub has to exceed a minimum pressure generally referred to as the phonation threshold pressure. This threshold pressure, as well as the Psub range, varies substantially with pitch and, presumably, also with vocal fold thickness. Comparisons between subjects with different threshold pressures and Psub ranges are facilitated by using the normalized excess pressure (Psen) (Titze 1992), representing an attempt to compensate for phonation threshold differences. 6 For obtaining a detailed view of how Psub influences the voice source a series of different Psub values needs to be analyzed. In Papers C, D and E, the singers were asked to sing from loudest to softest degree of vocal loudness at different F0s. This yielded a set of Psub values within each singer s total vocal loudness range. Then, ten equally spaced Psub values, within the singer s total Psub range, were selected. However, phonation threshold pressure is sometimes difficult to determine accurately, and errors easily result in quite misleading estimations of the Psen range. In such cases a better and simpler alternative is to express Psub as a percentage of the subject s total Psub range. This however requires access to a fair number of pressure values. Thus, Psub data can be expressed as (1) the actual pressure in cm H20, (2) as Psen, and (3) normalized with respect to the Psub range. Larynx and phonation Cartilages Figure 1. Front view of the larynx (from Netter F, Atlas of Human Anatomy 2nd ed. Novartis, East Hanover, New Jersey. 1997) The larynx is a cartilaginous structure located between the top of the trachea, the tube leading from the lungs, and the hyoid bone (see Figure 1). It is composed of cartilages connected by ligaments and muscles. The cricoid is the uppermost cartilage of the trachea, immediately below the thyroid. The cricoid has the shape of a complete signet ring, as opposed to the other hoarseshoe shaped tracheal cartilages, and its back is larger than its front. On top of the posterior signet part ride the much smaller arytenoid cartilages. They are shaped somewhat like triangles and can to a certain extent rotate vertically and horizontally, as well as slide posteriorly and anteriorly on the cricoid cartilage (Laver 1980). The thyroid is the big shield like cartilage protecting the larynx 7 which, in adult males, is protruding and is frequently referred to as the Adam s apple. The hyoid bone is the uppermost part of the laryngeal structure and is attached to the skull and the lower mandible. The epiglottis is the flap of cartilage lying behind the tongue and in front of the entrance to the larynx. At rest, the epiglottis is upright and allows air to pass through the larynx and into the rest of the respiratory system. During swallowing, it folds back to cover the entrance to the larynx, preventing food and drink from entering the trachea. The small tube inside the larynx is called the epilarynx tube. Vocal folds Inside the larynx, the true vocal folds and the ventricular folds are formed by the thyroarytenoid muscle. The true vocal folds are a complex structure containing muscles as well as layers of tissue. The body is the vocalis and thyroarytenoid muscles, anteriorly attached to the thyroid and posteriorly to the processes of the arytenoids (see Figure 2). Figure 2. Laryngeal muscles. (from H M. Tucker, The Larynx, Thieme 1987) Figure 3. Vocal fold structure. (from Hirano, 1974) 8 The cover, as described by Hirano (Hirano 1974 ; Hirano 1977), is composed of a microscopic five layered structure. The deep lamina propria is a fiber structure closest to the vocalis muscle. The intermediate lamina propria provides elasticity to the vocal fold. The superficial lamina propria also called Reinke s space consists of a gelatin like substance, and the outermost layer is the squamous epithelium which serves to protect the underlying tissue and help regulate vocal fold hydration (see Figure 3). With respect to the different stiffness characteristics, the folds can also be divided into three subgroups, the mucosa (the cover) that includes the epithelium and the superficial lamina propria, the vocalis ligament (transition) including the intermediate lamina propria and the deep lamina propria, and the body of the vocal fold, i.e., the vocalis muscle. Due to the vocal fold structure the opening and closing of the glottis, the air space between the folds, is complex. Glottal adduction, the action which closes the glottis, involves at least three muscular functions. The contraction of the lateral cricoarytenoid muscle swivels the arytenoid cartilages anteriorly and medially which adducts the vocal folds. The interarytenoids and the transvserse arytenoids help to close the posterior part of the glottis by a lateral gliding action (Laver 1980). Contraction of the lateral thyroarytenoid muscles produces medial compression of the glottis thus augmenting glottal adduction (van den Berg 1968). Vocal fold abduction is the muscular action that opens the glottis. It is normally performed by a single muscle pair, the posterior cricoarytenoids. Their contraction rotates the arytenoids outwards such that the vocal folds separate. Two muscles regulate the stiffness in the vocal folds, the vocalis and the criocothyroid muscles (Hirano et al. 1970), which affects the fundamental frequency (F0). Vocal fold length is mainly regulated by the paired cricothyroid muscles which when contracted stretches the folds by tipping the thyroid downwards towards the criciod cartilage. Contraction of the vocalis thickens the vocal folds, particularly at low F0, which also thickens the loose cover tissue. If the vocal folds are stiffened F0 is increased. Hence, lower F0 is characterized by shorter, thicker and more flapping vocal folds and higher F0 by longer, thinner and stiffer folds. Thus Psub needs to be adjusted to the current circumstances. Vocal fold length differs between the genders and is typically between mm in adult males and between 9 13 mm in adult females. This brings consequences for the pitch range; the longer the folds, the lower the pitch. In normal speech the typical F0 range for males is Hz, and for females Hz. Voice source The voice source is the pulsating transglottal airflow. A buzzing source sound is generated by the periodic train of flow pulses, produced as the vibrating vocal folds chop the steady air stream from the lungs. Vocal fold vibration starts when there is appropriate balance between the Psub and the muscular tension in the vocal folds. The myoelastic aerodynamic theory (van den Berg 1958), explains phonation as the result of three major factors, (1)
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