Estill Voice Training

Last updated
Estill Voice Training
AbbreviationEVT
Formation1988;36 years ago (1988)
FounderJo Estill
HeadquartersPittsburgh, Pennsylvania
President
Kimberly Steinhauer
Parent organization
Estill Voice International, LLC
Websitewww.estillvoice.com

Estill Voice Training (often abbreviated EVT) is a program for developing vocal skills based on analysing the process of vocal production into control of specific structures in the vocal mechanism. [1] By acquiring the ability to consciously move each structure the potential for controlled change of voice quality is increased. [2]

Contents

The system was established in 1988 [3] by American singing voice specialist Jo Estill, [4] who had been researching in this field since 1979. [5] [6] Estill's research led to a series of vocal manoeuvres to develop specific control over individual muscle groups within the vocal mechanism. [7] [8] [9] [10] Soto-Morettini quotes Estill as saying the great strength of her method is that it can be used for any style of music, [11] and speech and language therapists describe the exercises as valuable to voice therapy as well as singing, [12] in both professional and non-professional voice use, [7] offering an approach for therapeutic intervention. [13] Estill Voice Training is a trademark of Estill Voice International, LLC.

Operating principles

Power, source and filter: Estill Voice Training partitions the vocal system into the three components power, source and filter [14] 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). [15] The focus of Estill Voice Training is on the source and filter components of the vocal system and the interactions between them. [16]

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. [17] [18] Estill Voice Training has a focus on the "craft" aspect and hence has also been known as "Estill voice craft" by some practitioners. [3]

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. [7] This approach enables a speaker or singer to recognize, locate and control the degree of effort involved in voice production. [19]

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. [20] 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 [10] [21] vocal exercises or "figures for voice" (named after the "compulsory figures" that figure skaters use to demonstrate proficiency). [7] [22] [8] 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. [2] For example, the figure for velum (soft palate) control involves moving the velum through raised, partially lowered and lowered positions. [23] The thirteen Figures for Voice are:

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. [24] 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." [8]

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 [25] where a sound is produced across the entire vocal range. [26] Other figures are historically part of the model including vocal fold mass [7] which is now part of true vocal fold body-cover control, vocal fold plane [7] which is now part of true vocal folds body-cover control and exercises for falsetto quality, and pharyngeal width [2] [27] 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: [28] [29] 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. [30]

False Vocal Folds Control: Estill Voice Training identifies three possible positions of the false vocal folds: constricted, mid and retracted. [31] This figure is helpful in identification of glottal and ventricular constriction. Its concepts and options are valuable to voice therapy as well as singing. [12] The silent laugh technique, developed into an exercise by Jo Estill, is widely cited as reducing false vocal fold constriction. [32] [33] [23] [34] [35] [36] [37]

True Vocal Folds: Body-Cover Control: The 'body-cover theory' of vocal fold structure was introduced by Hirano in 1977. [38] 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. [29] [8] [39] 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. [40] This figure was formerly known as vocal fold mass. [7] [2]

Thyroid Cartilage Control: This figure demonstrates control of the position or tilt of the thyroid cartilage [2] [27] through engagement or disengagement of the cricothyroid muscle. [41] The speaker or singer can tilt the thyroid cartilage by adopting the posture of crying or sobbing, [42] or making a soft whimpering noise, like a small dog whining. [43] 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. [41]

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. [44]

Larynx Control: This figure trains raising and lowering of the larynx [8] influencing resonance. This figure was formerly known as the larynx height figure.

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. [23] [39] Dinah Harris writes, "Estill has excellent exercises for learning palatal control." [23]

Tongue Control: This figure demonstrates the influences of different tongue postures, such as compressed. [45] [39] 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. [46] Control of the tongue can have subtle resonance changes and give greater flexibility to the range. [45]

Aryepiglottic Sphincter 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. [47] [48] Estill suggests that this laryngeal tube creates a separate resonator that is responsible for the extra brightness in phonation. [49]

Jaw Control: The jaw figure demonstrates the subtle resonance changes in voice production that are associated with different positions or postures of the jaw. [50]

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. [51]

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. [52]

Torso Control: Torso anchoring stabilises the body and breath. [53] [54] 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.' [55]

Voice qualities

Estill Voice Training incorporates six 'voice qualities' [56] 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, [57] and variations on them. [27] 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). [43] The six voice qualities are: [58]

Voice qualities are taught on the course 'Level Two: Figure Combinations for Six Voice Qualities' that typically lasts two days.

Speech: Speech quality is often termed modal speech by voice scientists or chest voice by singers. [59] [60] Speech quality includes thick vocal folds and a neutral/mid larynx position. [61]

Falsetto: In Estill Voice Training terminology, the term falsetto has a meaning distinct from falsetto as a male vocal register in Western classical terminology. This quality is produced with stiff vocal fold body cover, neutral/mid larynx position, and aspirate vocal fold onset. [62]

Sob: Sob quality is a soft and dark sound, associated with the sobbing cry of an adult who mourns. [63] [64] Sob quality is produced on a lowered larynx and thinned vocal folds. [43] Sob quality releases glottal hyperadduction and medial compression, lowers the larynx and releases pharyngeal constriction. [23] Mary Hammond says that young performers find low larynx and sob quality less familiar. [65] Cry quality is a permutation of sob quality adopting a higher laryngeal position. [56]

Twang: The key to twang quality is a narrowing of the epilarynx via a narrowing or constriction of the aryepiglottic sphincter. [66] [27] [67] 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. [66] 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. [49] Twang quality may be nasalized or oral, as differentiated by an open or closed velopharyngeal port. [47] Estill suggests setting the vocal tract initially by imitating a cat yowling, ducks quacking, and other exercises. [49] [66]

Opera: Opera quality is a complex set-up including a mix of speech quality and twang quality with a tilted thyroid cartilage, lowered larynx. [67]

Belting: Belting or belt quality is a complex setup combining speech quality, twang quality, a tilted cricoid cartilage and raised larynx. [67] Twang is an important component in belt quality. [49] Gillyanne Kayes writes, 'Belting is not harmful if you are doing it right. Jo Estill has described it as "happy yelling".' [68] Belt quality also uses clavicular breathing and has the longest closed phase [69] with the highest subglottic pressure and the greatest glottic resistance. [70]

Certification

Estill Voice International governs the Estill Voice Training Certification Programme. There are three forms of Estill Voice Training certification available for individuals:[ citation needed ]

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. [71] 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." [72] 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." [73] The following list gives some examples of the application of Estill Voice Training in a range of disciplines:

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.' [86]

Criticism

Estill Voice Training has been criticised[ by whom? ] for not including 'breathing' and the related abdominal support within the system, and some of the uses of anchoring for classical singing, [8] [2] although Shewell cites Jo Estill as suggesting breath work as unnecessary if the Figures for Voice are well practiced. [4]

Notes

  1. ↑ Shewell 2009, p. 335.
  2. 1 2 3 4 5 6 Mathieson 2001, p. 495.
  3. 1 2 Estill Voice International, LLC 2010a.
  4. 1 2 Shewell 2009, p. 143.
  5. ↑ Estill & Colton 1979.
  6. ↑ Colton & Estill 1979.
  7. 1 2 3 4 5 6 7 Harris et al. 1998, p. 171.
  8. 1 2 3 4 5 6 Chapman 2006, p. 257.
  9. ↑ Houseman 2002, p. 11.
  10. 1 2 3 Calvi 2007.
  11. ↑ Soto-Morettini 2006, p. xvi.
  12. 1 2 Harris et al. 1998, p. 177.
  13. ↑ Martin & Lockhart 2000, p. 100.
  14. ↑ McDonald Klimek 2007.
  15. ↑ Obert & Chicurel 2005, p. 8.
  16. ↑ Sundberg 1987, p. 92.
  17. 1 2 Tobolski 2002, p. 19.
  18. ↑ Estill 2010.
  19. ↑ Chapman 2006, pp. 62–63.
  20. ↑ McDonald Klimek 2005a, p. 7.
  21. ↑ Golda 2010a, p. 29.
  22. ↑ Chapman 2006, p. 73.
  23. 1 2 3 4 5 Harris et al. 1998, p. 232.
  24. ↑ Olson 2001, p. 31.
  25. ↑ Harris et al. 1998, p. 235.
  26. ↑ McDonald Klimek 2005a, p. 57.
  27. 1 2 3 4 Harris et al. 1998, p. 172.
  28. ↑ Harris et al. 1998, p. 233.
  29. 1 2 Golda 2010b, p. 32.
  30. ↑ Harris et al. 1998, p. 165.
  31. ↑ Shewell 2009, p. 165.
  32. ↑ Citardi, Yanagisawa & Estill 1996.
  33. ↑ Kayes 2000, p. 14.
  34. ↑ Houseman 2002, p. 140.
  35. ↑ Springer 2007.
  36. ↑ Mitchell et al. 2003, p. 177.
  37. ↑ Shewell 2009, pp. 333 and 337.
  38. ↑ Obert & Chicurel 2005, p. 22.
  39. 1 2 3 Newham 1998, p. 68.
  40. ↑ McDonald Klimek 2005a, pp. 43.
  41. 1 2 McDonald Klimek 2005a, pp. 51–56.
  42. ↑ Speed 2001.
  43. 1 2 3 Harris et al. 1998, p. 175.
  44. ↑ McDonald Klimek 2005a, pp. 59–64.
  45. 1 2 McDonald Klimek 2005a, pp. 79–85.
  46. ↑ Diamond Rio 2009, pp. 240–241.
  47. 1 2 McDonald Klimek 2008, p. 95.
  48. ↑ Nair 1999, p. 64.
  49. 1 2 3 4 Harris et al. 1998, p. 181.
  50. ↑ McDonald Klimek 2005a, pp. 93–98.
  51. ↑ McDonald Klimek 2005a, pp. 99–103.
  52. ↑ McDonald Klimek 2005a, p. 105.
  53. ↑ Kayes 2004, p. 75.
  54. ↑ Olson 2001, p. 32.
  55. ↑ Kayes 2000, p. 69.
  56. 1 2 Kayes 2000, p. 153.
  57. ↑ Brown 1996, p. 180.
  58. ↑ Pinksterboer 2008, pp. 108–9.
  59. ↑ McDonald Klimek 2005b, p. 11.
  60. ↑ Verdolini & Krebs 1999, p. 228.
  61. ↑ Kayes 2004, p. 157.
  62. ↑ Jungr 2002, p. 105.
  63. ↑ McDonald Klimek 2005b, p. 31.
  64. ↑ Houseman 2002, p. 138.
  65. ↑ Melton 2007, p. 79.
  66. 1 2 3 Lombard & Steinhauer 2005, p. 295.
  67. 1 2 3 Kayes 2004, p. 158.
  68. ↑ Kayes 2004, p. 163.
  69. ↑ Sundberg, Gramming & Lovetri 1991, p. 60.
  70. ↑ McNaughton 2002, p. 5.
  71. ↑ Estill Voice International, LLC 2010c.
  72. ↑ Melton 2007, p. 194.
  73. ↑ Shewell 2009, p. 483.
  74. ↑ Diamond Rio 2009, pp. 237–244.
  75. 1 2 Lipton & Reeve 2003.
  76. ↑ Bell & Chicurel 2008, p. 117.
  77. ↑ Royal Academy of Music 2010, p. 17.
  78. ↑ Flinders University 2008, pp. 37–41.
  79. ↑ Flinders University 2010, p. 48.
  80. ↑ London College of Music 2009, pp. 20–21.
  81. ↑ "Major Requirements". Saint Mary's College. Retrieved 2021-11-23.
  82. ↑ Motherwell College, p. 158.
  83. ↑ Harris et al. 1998, p. 236.
  84. ↑ Rattenbury, Carding & Finn 2004.
  85. ↑ Lloyd 2009, p. 17.
  86. ↑ Soto-Morettini 2006, p. xv.

Related Research Articles

<span class="mw-page-title-main">Glottis</span> Opening between the vocal folds

The glottis is the opening between the vocal folds. The glottis is crucial in producing sound from the vocal folds.

The term phonation has slightly different meanings depending on the subfield of phonetics. Among some phoneticians, phonation is the process by which the vocal folds produce certain sounds through quasi-periodic vibration. This is the definition used among those who study laryngeal anatomy and physiology and speech production in general. Phoneticians in other subfields, such as linguistic phonetics, call this process voicing, and use the term phonation to refer to any oscillatory state of any part of the larynx that modifies the airstream, of which voicing is just one example. Voiceless and supra-glottal phonations are included under this definition.

<span class="mw-page-title-main">Human voice</span> Sound made by a human being using the vocal tract

The human voice consists of sound made by a human being using the vocal tract, including talking, singing, laughing, crying, screaming, shouting, humming or yelling. The human voice frequency is specifically a part of human sound production in which the vocal folds are the primary sound source.

<span class="mw-page-title-main">Larynx</span> Voice box, an organ in the neck of amphibians, reptiles, and mammals

The larynx, commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about 4–5 centimeters in diameter. The larynx houses the vocal cords, and manipulates pitch and volume, which is essential for phonation. It is situated just below where the tract of the pharynx splits into the trachea and the esophagus. The word 'larynx' comes from the Ancient Greek word lárunx ʻlarynx, gullet, throatʼ.

The field of articulatory phonetics is a subfield of phonetics that studies articulation and ways that humans produce speech. Articulatory phoneticians explain how humans produce speech sounds via the interaction of different physiological structures. Generally, articulatory phonetics is concerned with the transformation of aerodynamic energy into acoustic energy. Aerodynamic energy refers to the airflow through the vocal tract. Its potential form is air pressure; its kinetic form is the actual dynamic airflow. Acoustic energy is variation in the air pressure that can be represented as sound waves, which are then perceived by the human auditory system as sound.

<span class="mw-page-title-main">Singing</span> Act of producing musical sounds with the voice

Singing is the act of creating musical sounds with the voice. A person whose profession is singing is called a singer, artiste or vocalist. Singers perform music that can be sung with or without accompaniment by musical instruments. Singing is often done in an ensemble of musicians, such as a choir. Singers may perform as soloists or accompanied by anything from a single instrument up to a symphony orchestra or big band. Many styles of singing exist throughout the world.

Falsetto is the vocal register occupying the frequency range just above the modal voice register and overlapping with it by approximately one octave.

Head voice is a term used within vocal music. The use of this term varies widely within vocal pedagogical circles and there is currently no one consistent opinion among vocal music professionals in regard to this term. Head voice can be used in relation to the following:

<span class="mw-page-title-main">Belting (music)</span> Singing technique

Belting is a specific technique of singing by which a singer carries their chest voice above their break or passaggio with a proportion of head voice. Belting is sometimes described as "high chest voice" or "mixed voice", although if this is done incorrectly, it can potentially be damaging for the voice. It is often described as a vocal register, although this is also technically incorrect; it is rather a descriptive term for the use of a register.

<span class="mw-page-title-main">Bogart–Bacall syndrome</span> Voice disorder caused by abuse or overuse of the vocal cords

Bogart–Bacall syndrome (BBS) is a voice disorder that is caused by abuse or overuse of the vocal cords.

A hoarse voice, also known as dysphonia or hoarseness, is when the voice involuntarily sounds breathy, raspy, or strained, or is softer in volume or lower in pitch. A hoarse voice can be associated with a feeling of unease or scratchiness in the throat. Hoarseness is often a symptom of problems in the vocal folds of the larynx. It may be caused by laryngitis, which in turn may be caused by an upper respiratory infection, a cold, or allergies. Cheering at sporting events, speaking loudly in noisy environments, talking for too long without resting one's voice, singing loudly, or speaking with a voice that is too high or too low can also cause temporary hoarseness. A number of other causes for losing one's voice exist, and treatment is generally by resting the voice and treating the underlying cause. If the cause is misuse or overuse of the voice, drinking plenty of water may alleviate the problems.

"Voice therapy" or "voice training" refers to any non-surgical technique used to improve or modify the human voice. Because voice is a social cue to a person's sex and gender, transgender people may frequently undertake voice training or therapy as a part of gender transitioning in order to make their voices sound more typical of their gender, and therefore increase their likelihood of being perceived as that gender. Having voice and speech characteristics align with one's gender identity is often important to transgender individuals, whether their goal be feminization, neutralization or masculinization. Voice therapy can be seen as an act of gender- and identity-affirming care, in order to reduce gender dysphoria and gender incongruence, improve the self-reported wellbeing and health of transgender people, and alleviate concerns over an individual being recognized as transgender.

Chest voice is a term used within vocal music. The use of this term varies widely within vocal pedagogical circles and there is currently no one consistent opinion among vocal music professionals in regard to this term. Chest voice can be used in relation to the following:

<span class="mw-page-title-main">Vestibular fold</span> Part of the larynx

The vestibular fold is one of two thick folds of mucous membrane, each enclosing a narrow band of fibrous tissue, the vestibular ligament, which is attached in front to the angle of the thyroid cartilage immediately below the attachment of the epiglottis, and behind to the antero-lateral surface of the arytenoid cartilage, a short distance above the vocal process.

<span class="mw-page-title-main">Vocal pedagogy</span> Study of the art and science of voice instruction

Vocal pedagogy is the study of the art and science of voice instruction. It is used in the teaching of singing and assists in defining what singing is, how singing works, and how singing technique is accomplished.

Puberphonia is a functional voice disorder that is characterized by the habitual use of a high-pitched voice after puberty, hence why many refer to the disorder as resulting in a 'falsetto' voice. The voice may also be heard as breathy, rough, and lacking in power. The onset of puberphonia usually occurs in adolescence, between the ages of 11 and 15 years, at the same time as changes related to puberty are occurring. This disorder usually occurs in the absence of other communication disorders.

Vocal resonance may be defined as "the process by which the basic product of phonation is enhanced in timbre and/or intensity by the air-filled cavities through which it passes on its way to the outside air." Throughout the vocal literature, various terms related to resonation are used, including: amplification, filtering, enrichment, enlargement, improvement, intensification, and prolongation. Acoustic authorities would question many of these terms from a strictly scientific perspective. However, the main point to be drawn from these terms by a singer or speaker is that the result of resonation is to make a better sound, or at least suitable to a certain esthetical and practical domain.

Professor Janice L. Chapman AUA [born January 1938 ]OAM is an Australian-born soprano, voice researcher, and vocal consultant. She is the author of Singing and Teaching Singing: A Holistic Approach to Classical Voice first published by Plural Publishing Inc. at the end of 2005, and she has contributed to papers in the Journal of Voice, The Journal of the Acoustical Society of America and Australian Voice. She is also a professor of voice at the Guildhall School of Music and Drama in London.

<span class="mw-page-title-main">Jo Estill</span> American singer (1921–2010)

Josephine Antoinette Estill, known as Jo Estill, was an American singer, singing voice specialist and voice researcher. Estill is best known for her research and the development of Estill Voice Training, a programme for developing vocal skills based on deconstructing the process of vocal production into control of specific structures in the vocal mechanism.

Flaccid dysarthria is a motor speech disorder resulting from damage to peripheral nervous system or lower motor neuron system. Depending on which nerves are damaged, flaccid dysarthria affects respiration, phonation, resonance, and articulation. It also causes weakness, hypotonia, and diminished reflexes. Perceptual effects of flaccid dysarthria can include hypernasality, imprecise consonant productions, breathiness of voice, and affected nasal emission.

References

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.