Estill Voice Training
|Estill Voice International, LLC|
Estill Voice Training (often abbreviated EVT) is a programme for developing vocal skills based on analysing the process of vocal production into control of specific structures in the vocal mechanism. By acquiring the ability to consciously move each structure the potential for controlled change of voice quality is increased.
British speech and language therapist Sara Harris writes:
The work allows singing/voice teachers, voice coaches, and speech and language therapists to identify and resolve specific vocal problems that have resulted in fatigue or damage to the vocal folds. Many of the manoeuvers are already familiar to speech therapists as they have been adapted from traditional techniques but synthesized into an extremely creative system. The application of the system to dysphonic patients produces excellent results and the therapist will gain great confidence in their own voice use having mastered the manoeuvres and qualities themselves.— Sara Harris, The Voice Clinic Handbook, Speech Therapy for Dysphonia pp 171–172
The system was established in 1988 by American singing voice specialist Jo Estill, who had been researching in this field since 1979. Estill's research led to a series of vocal manoeuvres to develop specific control over individual muscle groups within the vocal mechanism. Soto-Morettini quotes Estill as saying the great strength of her method is that it can be used for any style of music, and speech and language therapists describe the exercises as valuable to voice therapy as well as singing, in both professional and non-professional voice use, offering an approach for therapeutic intervention. Estill Voice Training is a trademark of Estill Voice International, LLC.
Power, Source and Filter: Estill Voice Training partitions the vocal system into the three components power, source and filter extending the existing source-filter model of speech production. 'Power' is the source of energy producing the sound (typically the respiratory system causing air to be expelled from the lungs). 'Source' is the component that vibrates to create the sound waves (the vocal folds). 'Filter' is the shaping of the sound waves to create the final result (the vocal tract). The focus of Estill Voice Training is on the source and filter components of the vocal system and the interactions between them.
Craft, Artistry and Performance Magic: Estill Voice Training separates the use of voice into the 'craft' of having control over the vocal mechanism, the 'artistry' of expression relative to the material and context, and the 'performance magic' of a speaker or singer connecting with their audience. Estill Voice Training has a focus on the 'craft' aspect and hence has also been known as Estill Voice Craft by some practitioners.
Effort Levels: Estill Voice Training uses the identification and quantification of the level of work or 'effort' required for speaking and singing to help develop kinesthetic feedback. This approach enables a speaker or singer to recognize, locate and control the degree of effort involved in voice production.
Dynamical Systems Theory and Attractor States: The human vocal system is extremely complex, involving interactions between breath flow, moving structures, resonators and so on. Estill Voice Training draws on a branch of applied mathematics known as dynamical systems theory that helps to describe complex systems. One key concept Estill Voice Training takes from dynamical systems theory is the notion that complex systems can have attractor states. Attractor states are states to which a complex system tends towards, or is attracted to, over time. When applied to the human vocal system, Estill Voice Training proposes there are configurations of the vocal system that are attractor states, which the speaker or singer uses habitually or tend towards. For example, a subject whose attractor state is for their velum (also known as the soft palate) to be in a raised position may find it requires more conscious effort to create a nasal sound than someone else whose attractor state is for their velum to be in the lowered position.
Figures for voice
In Estill Voice Training there are thirteen vocal exercises or 'Figures for Voice' (named after the 'compulsory figures' that figure skaters use to demonstrate proficiency). Each exercise or 'figure' establishes control over a specific structure of the vocal mechanism, in isolation, by moving the structure through a number of positions. For example, the figure for velum (soft palate) control involves moving the velum through raised, partially lowered and lowered positions. The thirteen Figures for Voice are:
- True Vocal Folds: Onset/Offset Control
- False Vocal Folds Control
- True Vocal Folds: Body-Cover Control
- Thyroid Cartilage Control
- Cricoid Cartilage Control
- Larynx Control
- Velum Control
- Tongue Control
- Aryepiglottic Spincter Control
- Jaw Control
- Lips Control
- Head and Neck Control
- Torso Control
These Figures for Voice exercises have a focus basic anatomy and vocal physiology, a knowledge of which helps encourage deductions on reducing constriction and healthy voice decisions. Janice Chapman, the operatic singer, voice teacher and researcher, writes "Estill figures lead to a much greater freedom and flexibility in the demanding work of the singer and actor."
Figures for Voice are taught on the course 'Level One: Figures for Voice' that typically lasts three days. In addition to the thirteen Figures for Voice, Estill Voice Training also includes the 'Siren' exercise where a sound is produced across the entire vocal range. Other figures are historically part of the model including vocal fold mass which is now part of true vocal fold body-cover control, vocal fold plane which is now part of true vocal folds body-cover control and exercises for falsetto quality, and pharyngeal width which is now part of false vocal folds control and head and neck control.
True Vocal Folds: Onset/Offset Control: In this figure there are three options for coordinating expiration and vocal fold closure: glottal where the vocal folds are closed before expiration, smooth where vocal fold closure is synchronised with expiration, and aspirate where expiration precedes vocal fold closure. Learning to produce and apply different onsets marks the beginning of control over the vocal mechanism.
False Vocal Folds Control: Estill Voice Training identifies three possible positions of the false vocal folds: constricted, mid and retracted. This figure is helpful in identification of glottal and ventricular constriction. Its concepts and options are valuable to voice therapy as well as singing. The silent laugh technique, developed into an exercise by Jo Estill, is widely cited as reducing false vocal fold constriction.
True Vocal Folds: Body-Cover Control: The 'body-cover theory' of vocal fold structure was introduced by Hirano in 1977. This figure demonstrates the controlled use of the vocal folds in four body-cover configurations: on the thick edge, on the thin edge, in a stiff mode, or in a slack mode. These body-cover configurations change or modify the vibratory modes of the true vocal folds and, within the dynamical system of the human voice, effect the intensity of the sound produced and contribute to what are commonly labeled as the different human vocal registers. This figure was formerly known as vocal fold mass.
Thyroid Cartilage Control: This figure demonstrates control of the position or tilt of the thyroid cartilage through engagement or disengagement of the cricothyroid muscle. The speaker or singer can tilt the thyroid cartilage by adopting the posture of crying or sobbing, or making a soft whimpering noise, like a small dog whining. In Estill Voice training, it is proposed that the position of the thyroid cartilage influences not only pitch but also the quality and intensity of the sound produced.
Cricoid Cartilage Control: This figure demonstrates control of the position of the cricoid cartilage. In Estill Voice training it is proposed that specific positioning of the cricoid cartilage is a typical part of the vocal set-up for shouting and other high-intensity voice productions employing higher subglottic pressure.
Velum Control: This figure trains the velum (also known as the soft palate) and consists of exercises opening, partially closing and completely closing the velopharyngeal port to control the degree of nasality in the voice. Dinah Harris writes, "Estill has excellent exercises for learning palatal control."
Tongue Control: This figure demonstrates the influences of different tongue postures, such as compressed. As a practical example, Diane Sheets (Estill Voice Training Certified Course Instructor) worked on the interaction of tongue and larynx when dealing with the vocal problems of Marty Roe, lead vocalist of Diamond Rio. Control of the tongue can have subtle resonance changes and give greater flexibility to the range.
Aryepiglottic Spincter Control: This figure demonstrates the ability to control twang in the voice through conscious anteroposterior narrowing of the aryepiglottic sphincter in the upper epilarynx while avoiding constriction of the false vocal folds. Estill suggests that this laryngeal tube creates a separate resonator that is responsible for the extra brightness in phonation.
Jaw Control: The jaw figure demonstrates the subtle resonance changes in voice production that are associated with different positions or postures of the jaw.
Lips Control: This figure demonstrates various lip postures employed by speakers and singers and their subtle impact on vocal resonance through changing the length of the vocal tract.
Head and Neck Control: Head and neck anchoring involves bracing the skeletal structures of the head and neck gives a stable external framework for the smaller muscles that control the vocal tract.
Torso Control: Torso anchoring stabilises the body and breath. Gillyanne Kayes writes, 'Techniques for anchoring the tone have been described over the centuries by singers and teachers under a variety of names: support, singing from the back, singing from the neck, appoggiare, rooting, grounding and connecting the voice. In the Estill training model, I believe these techniques have been correctly identified as postural anchoring.'
Estill Voice Training incorporates six 'voice qualities' as mechanisms for demonstration of voice production control. The increased control developed through proficiency in the different Figures for Voice allows the singer or speaker to manipulate the vocal mechanism specifically to produce these arbitrary voice qualities, and variations on them. Essentially these voice qualities, such as 'Sob Quality' and 'Belt Quality', are constructed from moving the structures of the vocal mechanism into specific positions or combinations. For example, Sob Quality includes a low larynx position (the larynx figure) and thin vocal folds (the true vocal fold body & cover figure). The six voice qualities are:
- Twang (Oral and Nasal variations)
Voice qualities are taught on the course 'Level Two: Figure Combinations for Six Voice Qualities' that typically lasts two days.
Sob: Sob quality is a soft and dark sound, associated with the sobbing cry of an adult who mourns. Sob quality is produced on a lowered larynx and thinned vocal folds. Sob quality releases glottal hyperadduction and medial compression, lowers the larynx and releases pharyngeal constriction. Mary Hammond says that young performers find low larynx and sob quality less familiar. Cry quality is a permutation of sob quality adopting a higher laryngeal position.
Twang: The key to twang quality is a narrowing of the epilarynx via a narrowing or constriction of the aryepiglottic sphincter. Twang quality has been used by speakers and singer to boost vocal resonance or 'squillo' and is referred to as the speaker's ring or singer's formant. The quality is excellent when teaching safe shouting and at cutting through background noise, increasing clarity of the voice, and is taught to both singers and actors to enable them to be heard clearly in large auditoria without vocal strain. Twang quality may be nasalized or oral, as differentiated by an open or closed velopharyngeal port. Estill suggests setting the vocal tract initially by imitating a cat yowling, ducks quacking, and other exercises.
Opera: Opera quality is a complex set-up including a mix of speech quality and twang quality with a tilted thyroid cartilage, lowered larynx.
Belting: Belting or belt quality is a complex setup combining speech quality, twang quality, a tilted cricoid cartilage and raised larynx. Twang is an important component in belt quality. Gillyanne Kayes writes, 'Belting is not harmful if you are doing it right. Jo Estill has described it as "happy yelling".' Belt quality also uses clavicular breathing and has the longest closed phase with the highest subglottic pressure and the greatest glottic resistance.
Estill Voice International governs the Estill Voice Training Certification Programme. There are three forms of Estill Voice Training certification available for individuals:
- Estill Figure Proficiency (EFP) is awarded to individuals who can demonstrate the basic options for voice control taught in Estill Voice Training™ Level One (Figures for Voice Control), and Level Two (Figure Combinations for Six Voice Qualities) courses with appropriate Hand Signals.
- Estill Master Trainer (EMT) qualifies an individual to teach Estill Voice Training within their private studio, course practice sessions or classroom setting. The certification is a two-stage examination including written and voice control components, and observed teaching.
- Estill Mentors and Course Instructors (EMCI) follows Estill Master Trainer, qualifying an individual to teach Estill Voice Training in public courses, seminars and conferences. The certification is a two-stage examination including written and oral components and observed presentations.
Influence, adoption and application
Estill Voice Training has been adopted by voice professionals worldwide and a list of certified instructors is published by Estill Voice International. Joan Melton describes the Estill Voice Training terminology as a part of the language of singing teachers in Australia, with terms such as twang and anchoring in common use, although "the Estill language is heard somewhat less frequently in the UK and only occasionally in the United States." Freelance voice teacher and speech and language therapist Christina Shewell writes, "Estill Voice Training clarifies many of the complex vocal tract options that shape the style of a singers voice, explaining and demonstrating different combinations of structural conditions, and many singing teachers use the system as part of their teaching." The following list gives some examples of the application of Estill Voice Training in a range of disciplines:
- Pop Singing: Maureen Scott is a Certified Master Teacher whose clients include Mika and The Enemy.
- Country Singing: Diane Sheets is a Certified Course Instructor whose clients have included Marty Roe of Nashville Country Band Diamond Rio.
- Acting: Estill Voice Training has been integrated into the training of actors at Mountview Academy of Theatre Arts in London.
- Musical Theatre: Faculty teaching on Musical Theatre training courses reference their Estill Voice Training certification. Examples include Steven Chicurel, Certified Course Instructor with testing privileges and service distinction, who is an associate professor of theatre at the University of Central Florida, and Anne-Marie Speed, Certified Course Instructor with testing privileges and service distinction, who teaches spoken voice on the Musical Theatre course at the Royal Academy of Music in London.
- Educational Curriculum: Educational institutions have adopted Estill Voice Training terminology and exercises into their curriculum. Examples include the Drama Centre at Flinders University in Adelaide, South Australia, where the Estill-based vocal technique is taught; London College of Music in its guidelines on the suggested development of vocal technique, as part of the music theatre syllabus, uses Estill Voice Training terminology; Motherwell College, Scotland, includes Estill Voice Training in its BA Honours Musical Theatre and BA Honours Acting programmes; and at the prestigious Bird College in London. and the Voice Performance and Musical Theatre programmes at Mars Hill College, North Carolina, include Estill Voice Training in their curriculum.
- Clinical Voice Therapy: Dinah Harris, contributor to The Voice Clinic Handbook, recommends learning Estill Voice Training as it provides many useful tools for those working in a voice clinic. Rattenbury, Carding and Finn present a study that used a range of Figures for Voice exercises as prognostic indicators and voice therapy treatment techniques.
- Community Choirs: Thomas Lloyd, Artistic Director of the Bucks County Choral Society, writes that he has "seen and heard results related to sound, dynamic range, consistency of support, and vocal color with [his] choirs, especially with [his] untrained singers."
Soto-Morettini writes that, 'although the Estill method can be very complex, there are a number of simple things that students can learn quickly — and that these simple things can go a long way towards clearing up the confusion that attends some vocal training.'
Estill Voice Training has been criticised for not including 'breathing' and the related abdominal support within the system, and some of the uses of anchoring for classical singing, although Shewell cites Jo Estill as suggesting breath work as unnecessary if the Figures for Voice are well practiced.
- Shewell 2009, p. 335.
- Mathieson 2001, p. 495.
- Estill Voice International, LLC 2010a.
- Shewell 2009, p. 143.
- Estill & Colton 1979.
- Colton & Estill 1979.
- Harris et al. 1998, p. 171.
- Chapman 2006, p. 257.
- Houseman 2002, p. 11.
- Calvi 2007.
- Soto-Morettini 2006, p. xvi.
- Harris et al. 1998, p. 177.
- Martin & Lockhart 2000, p. 100.
- McDonald Klimek 2007.
- Obert & Chicurel 2005, p. 8.
- Sundberg 1987, p. 92.
- Tobolski 2002, p. 19.
- Estill 2010.
- Chapman 2006, pp. 62–63.
- McDonald Klimek 2005a, p. 7.
- Golda 2010a, p. 29.
- Chapman 2006, p. 73.
- Harris et al. 1998, p. 232.
- Olson 2001, p. 31.
- Harris et al. 1998, p. 235.
- McDonald Klimek 2005a, p. 57.
- Harris et al. 1998, p. 172.
- Harris et al. 1998, p. 233.
- Golda 2010b, p. 32.
- Harris et al. 1998, p. 165.
- Shewell 2009, p. 165.
- Citardi, Yanagisawa & Estill 1996.
- Kayes 2000, p. 14.
- Houseman 2002, p. 140.
- Springer 2007.
- Mitchell et al. 2003, p. 177.
- Shewell 2009, pp. 333 and 337.
- Obert & Chicurel 2005, p. 22.
- Newham 1998, p. 68.
- McDonald Klimek 2005a, pp. 43.
- McDonald Klimek 2005a, pp. 51–56.
- Speed 2001.
- Harris et al. 1998, p. 175.
- McDonald Klimek 2005a, pp. 59–64.
- McDonald Klimek 2005a, pp. 79–85.
- Diamond Rio 2009, pp. 240–241.
- McDonald Klimek 2008, p. 95.
- Nair 1999, p. 64.
- Harris et al. 1998, p. 181.
- McDonald Klimek 2005a, pp. 93–98.
- McDonald Klimek 2005a, pp. 99–103.
- McDonald Klimek 2005a, p. 105.
- Kayes 2004, p. 75.
- Olson 2001, p. 32.
- Kayes 2000, p. 69.
- Kayes 2000, p. 153.
- Brown 1996, p. 180.
- Pinksterboer 2008, pp. 108–9.
- McDonald Klimek 2005b, p. 11.
- Verdolini & Krebs 1999, p. 228.
- Kayes 2004, p. 157.
- Jungr 2002, p. 105.
- McDonald Klimek 2005b, p. 31.
- Houseman 2002, p. 138.
- Melton 2007, p. 79.
- Lombard & Steinhauer 2005, p. 295.
- Kayes 2004, p. 158.
- Kayes 2004, p. 163.
- Sundberg, Gramming & Lovetri 1991, p. 60.
- McNaughton 2002, p. 5.
- Estill Voice International, LLC 2018b.
- Estill Voice International, LLC 2010c.
- Melton 2007, p. 194.
- Shewell 2009, p. 483.
- Diamond Rio 2009, pp. 237–244.
- Lipton & Reeve 2003.
- Bell & Chicurel 2008, p. 117.
- Royal Academy of Music 2010, p. 17.
- Flinders University 2008, pp. 37–41.
- Flinders University 2010, p. 48.
- London College of Music 2009, pp. 20–21.
- Motherwell College, p. 158.
- Harris et al. 1998, p. 236.
- Rattenbury, Carding & Finn 2004.
- Lloyd 2009, p. 17.
- Soto-Morettini 2006, p. xv.
- Bell, John; Chicurel, Steven R (2008). Music Theory for Musical Theatre. Lanham, Maryland: Scarecrow Press. ISBN 978-0-8108-5901-2.
- Brown, Oren (1996). Discover Your Voice: How to Develop Healthy Voice Habits. San Diego: Singular Publishing. ISBN 1-56593-704-X.
- Calvi, Nuala (2007-08-23). "The voice of reason". The Stage. London. p. 34. ISSN 0038-9099.
- Chapman, Janice (2006). Singing and Teaching Singing: A Holistic Approach to Classical Voice. San Diego: Plural Publishing. ISBN 1-59756-015-4.
- Citardi, Martin J; Yanagisawa, Eiji; Estill, Jo (July 1996). "Videoendoscopic Analysis of Laryngeal Function During Laughter". Annals of Otology, Rhinology, and Laryngology. St. Louis: Annals Publishing Company. 105 (7): 545–549. ISSN 0003-4894. OCLC 1481398.
- Colton, RH; Estill, J (June 1979). "Perceptual aspects of some voice qualities". The Journal of the Acoustical Society of America. New York: American Institute of Physics for the Acoustical Society of America. 65 (S1): S115. doi:10.1121/1.2016967. ISSN 0001-4966.
- Diamond Rio (2009). Beautiful Mess. With Tom Roland. Nashville, Tennessee: Thomas Nelson. ISBN 978-1-59555-268-6.
- Estill, J; Colton, RH (June 1979). "The identification of some voice qualities". The Journal of the Acoustical Society of America. New York: American Institute of Physics for the Acoustical Society of America. 65 (S1): S115. doi:10.1121/1.2016966. ISSN 0001-4966.
- Estill, Jo (1981). Lawrence, V, ed. Observations about the quality called 'Belting'. Transcripts of the 9th Symposium: Care of the Professional Voice. The Juilliard School, New York City.
- Estill, Jo (2010-09-01). Jo Speaks. Pittsburgh: Estill Voice International, LLC. Retrieved 2010-09-11.
- Flinders University Drama Centre Handbook 2008 (PDF). Flinders University. 2008. Retrieved 2010-12-11.
- Flinders University Drama Centre Handbook 2010 (PDF). Flinders University. 2010. Retrieved 2010-12-11.
- Golda, Lisa (July 2010a). "Deciphering Vocal Technique with Estill Voice Training" (PDF). Classical Singer. Draper, Utah: Classical Singer, Inc. 23 (7): 26–9. ISSN 1534-276X. OCLC 39776683. Retrieved 2010-10-24.
- Golda, Lisa (August 2010b). "Deciphering the Estill Voice Training Method Itself" (PDF). Classical Singer. Draper, Utah: Classical Singer, Inc. 23 (8): 32–3. ISSN 1534-276X. OCLC 39776683. Retrieved 2010-10-24.
- Harris, Tom; Harris, Sara; Rubin, John S; et al., eds. (1998). The Voice Clinic Handbook. London: Whurr Publishers Ltd. ISBN 978-1-86156-034-6.
- Houseman, Barbara (2002). Finding Your Voice: A Step-by-Step Guide For Actors. London: Nick Hern Books. ISBN 1-85459-659-4.
- Jungr, Barb (2002). "Vocal expression in the blues and gospel". In Moore, Allan. The Cambridge Companion to Blues and Gospel Music. Cambridge Companions to Music. Cambridge: Cambridge University Press. pp. 102–115. ISBN 978-0-521-80635-0.
- Kayes, Gillyanne (2000). Singing and the Actor (1st ed.). London: A & C Black. ISBN 0-7136-4888-0.
- Kayes, Gillyanne (2004). Singing and the Actor (2nd ed.). London: A & C Black. ISBN 0-7136-6823-7.
- Lloyd, Thomas (December 2009). "My Encounter with Estill Voice Training" (PDF). Troubadour: the Journal of ACDA Eastern Division. American Choral Directors Association Eastern Division. XVIII (2): 15–17. Retrieved 2010-10-24.
- Lombard, Lori E.; Steinhauer, Kimberly M. (2005). "A Novel Treatment for Hypophonic Voice: Twang Therapy". Journal of Voice. 21 (3): 294–299. doi:10.1016/j.jvoice.2005.12.006. PMID 16527452.
- Lipton, Rick; Reeve, Matthew (July 2003). Integration of Estill Voice Craft into Actor Training at Mountview Academy of Theatre Arts, London, UK. EVTS First World Symposium. Santa Rosa, California.
- London College of Music Examinations Syllabus for Graded, Step, Duet and Performance Diploma Examinations in Music Theatre 2009–2012 (PDF) (May 2009 ed.). London: Thames Valley University. 2009. Retrieved 2010-06-05.
- Martin, Stephanie; Lockhart, Myra (2000). Working with Voice Disorders. Bicester: Speechmark Publishing. ISBN 0-86388-489-X.
- Mathieson, Lesley (2001). Greene and Mathieson's The Voice and Its Disorders (6th ed.). London: Whurr. ISBN 1-86156-196-2.
- McDonald Klimek, Mary (2005a). Estill Voice Training System Level One: Compulsory Figures for Voice Control. Think Voice Series. With Kerrie Obert and Kimberly Steinhauer. Pittsburgh: Estill Voice Training Systems International, LLC. ISBN 978-0-9764816-2-1. OCLC 387072380.
- McDonald Klimek, Mary (2005b). Estill Voice Training System Level Two: Figure Combinations for Six Voice Qualities. Think Voice Series. With Kerrie Obert and Kimberly Steinhauer. Pittsburgh: Estill Voice Training Systems International, LLC. ISBN 978-0-9764816-1-4. OCLC 387072381.
- McDonald Klimek, Mary (2007). Estill Voice Model Applications in voice therapy. 27th World Congress of the International Association of Logopedics and Phoniatrics. Copenhagen, Denmark.
- McDonald Klimek, Mary (2008). "Using Twang". In Behrman, Alison; Haskell, John. Exercises for Voice Therapy. San Diego: Plural Publishing. ISBN 978-1-59756-231-7.
- Melton, Joan (2007). Singing in Musical Theatre: The Training of Singers and Actors (PDF). New York: Allworth Press. ISBN 978-1-58115-482-5. Retrieved 2010-06-18.
- Mitchell, Helen F; Kenny, Dianna T; Ryan, Maree; Davis, Pamela J (2003). "Defining 'open throat' through content analysis of experts' pedagogical practices" (PDF). Logoped Phoniatr Vocol. Taylor & Francis. 28 (4): 167–180. doi:10.1080/14015430310018856. ISSN 1401-5439. Retrieved 2011-03-09.
- Motherwell College Prospectus 2010/2011. Motherwell College.
- McNaughton, Elizabeth (2002). Breathing for Singing and its Vocal Pedagogy. Swindon: Phoenix Again. ISBN 0-9543165-0-9. OCLC 51234995.
- Nair, Garyth (1999). Voice-Tradition and Technology: A State-of-the-Art Studio. San Diego: Singular Publishing Group. ISBN 0-7693-0028-6.
- Newham, Paul (1998). "Vocal Function and Structure". Therapeutic Voicework: Principles and Practice for the Use of Singing as a Therapy. Art Therapies Series. London: Jessica Kingsley Publishers. ISBN 978-1-85302-361-3. OCLC 38463908.
- Obert, Kerrie B; Chicurel, Steven R (2005). Geography of the Voice (second ed.). Think Voice International. ISBN 978-0-9764816-0-7.
- Olson, Lise (2001). "Some Personal Discoveries Regarding Vocal Use in Stage Combat". In Dal Vera, Rocco. The Voice in Violence and Other Contemporary Issues in Professional Voice and Speech Training Presented by the Voice and Speech Review. Cincinnati: Voice and Speech Trainers Association, Inc. pp. 30–33. ISBN 978-1-55783-497-3.
- Pinksterboer, Hugo (2008). Tipbook Vocals : The Complete Guide (5th ed.). New York: Hal Leonard. ISBN 978-1-4234-5622-3. OCLC 225873891.
- Rattenbury, Helen J.; Carding, Paul N.; Finn, Paul (2004). "Evaluating the Effectiveness and Efficiency of Voice Therapy using Transnasal Flexible Laryngoscopy: A Randomized Controlled Trial". Journal of Voice. 18 (4): 522–33. doi:10.1016/j.jvoice.2004.01.003. Retrieved 2010-10-25.
- Royal Academy of Music: Musical Theatre Prospectus 2011 (PDF). Royal Academy of Music. August 2010. Retrieved 2011-03-10.
- Shewell, Christina (2009). Voice Work: Art and Science in Changing Voices. Wiley-Blackwell. ISBN 978-0-470-01992-4.
- Soto-Morettini, Donna (2006). Popular Singing: A Practical Guide to: Pop, Jazz, Blues, Country and Gospel. London: A & C Black. ISBN 978-0-7136-7266-4.
- Speed, Anne-Marie (April 2001). "The Singer's Speaking Voice". Communicating Voice. British Voice Association. 2 (3). Retrieved 2011-03-09.
- Springer, Gail (February 2007). "Shouting for Joy". The VASTA Voice. Voice and Speech Trainers Association, Inc. 3 (1). Retrieved 2011-03-09.
- Sundberg, Johan (1987). The Science of the Singing Voice. Illinois: Northern Illinois University Press. ISBN 0-87580-542-6.
- Sundberg, Johan; Gramming, Patricia; Lovetri, Jeannette (1991). "Comparisons of pharynx, source, formant and pressure characteristics in operatic and musical theatre singing" (PDF). Speech, Music and Hearing Quarterly Progress and Status Report. Stockholm, Sweden: KTH, CSC Computer Science and communication. 32 (2–3): 51–62. Retrieved 2010-06-18.
- Tobolski, Erica (2002). "Innovations in Voice Training: Exploring Additional Tools" (PDF). VASTA Newsletter. Voice and Speech Trainers Association, Inc. 16 (1): 18–19. Retrieved 2010-06-18.
- Verdolini, Katherine; Krebs, David (1999). "Some Considerations on the Science of Special Challenges in Voice Training". Voice-Tradition and Technology: A State-of-the-Art Studio. San Diego: Singular Publishing Group. ISBN 0-7693-0028-6.
- Estill Voice International, LLC (2010a). "History". Estill Voice International website. Retrieved 2010-09-11.
- Estill Voice International, LLC (2010b). "Estill Voice Training Certification Program". Estill Voice International website. Retrieved 2010-09-11.
- Estill Voice International, LLC (2010c). "Find an Instructor". Estill Voice International website. Retrieved 2010-10-21.