In speech science and phonetics, a formant is the spectral shaping that results from an acoustic resonance of the human vocal tract. However, in acoustics, the definition of a formant differs as it is defined as a peak, or local maximum, in the spectrum. For harmonic sounds, with this definition, it is therefore the harmonic partial, augmented by a resonance; the difference between these two definitions resides in whether "formants" characterise the production mechanisms of a sound or the produced sound itself. In practice, the frequency of a spectral peak can differ from the associated resonance frequency when, for instance, harmonics are not aligned with the resonance frequency. In most cases, this subtle difference is irrelevant and, in phonetics, formant can mean either a resonance or the spectral maximum that the resonance produces. Formants are measured as amplitude peaks in the frequency spectrum of the sound, using a spectrogram or a spectrum analyzer and, in the case of the voice, this gives an estimate of the vocal tract resonances.
In vowels spoken with a high fundamental frequency, as in a female or child voice, the frequency of the resonance may lie between the spaced harmonics and hence no corresponding peak is visible. A room can be said to have formants characteristic of that particular room, due to the way sound reflects from its walls and objects. Room formants of this nature reinforce themselves by emphasizing specific frequencies and absorbing others, as exploited, for example, by Alvin Lucier in his piece I Am Sitting in a Room. From an acoustic point of view, phonetics had a serious problem with the idea that length of vocal tract changed vowels, it was unclear how they could depend on frequencies when everyone from bass to soprano can make the same vowels. There had to be some way to normalize the frequencies. Hermann suggested a solution to this problem in 1894, coining the term “formant”. A vowel, according to him, is a special acoustic phenomenon, depending on the intermittent production of a special partial, or “formant”, or “characteristique”.
The frequency of the “formant” may vary a little without altering the character of the vowel. For a, for example, the “formant” may vary from 350 to 440 Hz in the same person. Formants are distinctive frequency components of the acoustic signal produced by singing; the information that humans require to distinguish between speech sounds can be represented purely quantitatively by specifying peaks in the amplitude or frequency spectrum. Most of these formants are produced by tube and chamber resonance, but a few whistle tones derive from periodic collapse of Venturi effect low-pressure zones; the formant with the lowest frequency is called F1, the second F2, the third F3. Most the two first formants, F1 and F2, are enough to disambiguate the vowel; the relationship between the perceived vowel quality and the first two formant frequencies can be appreciated by listening to "artificial vowels" that are generated by passing a click train through a pair of bandpass filters. Nasal consonants have an additional formant around 2500 Hz.
The liquid has an extra formant at 1500 Hz, whereas the English "r" sound is distinguished by a low third formant. Plosives modify the placement of formants in the surrounding vowels. Bilabial sounds cause a lowering of the formants; the time course of these changes in vowel formant frequencies are referred to as'formant transitions'. If the fundamental frequency of the underlying vibration is higher than a resonance frequency of the system the formant imparted by that resonance will be lost; this is most apparent in the example of soprano opera singers, who sing high enough that their vowels become hard to distinguish. Control of resonances is an essential component of the vocal technique known as overtone singing, in which the performer sings a low fundamental tone, creates sharp resonances to select upper harmonics, giving the impression of several tones being sung at once. Spectrograms are used to visualise formants. In spectrograms, it can be hard to distinguish formants from occurring harmonics when one sings.
However, one can hear the natural formants in a vowel shape through atonal techniques such as vocal fry. The first two formants are important in determining the quality of vowels, are said to correspond to the open/close and front/back dimensions, thus the first formant F1 has a higher frequency for an open vowel and a lower frequency for a close vowel. Vowels will always have four or more distinguishable formants. However, the first two formants are most important in determining vowel quality, this is displayed in terms of a plot of the first formant against the second formant, though this is not sufficient to capture some aspects of vowel quality, such as rounding. An example of how the vowels of a language or dialect may be plotted on a traditional auditory vow
Ivory Coast or Côte d'Ivoire the Republic of Côte d'Ivoire, is a country located on the south coast of West Africa. Ivory Coast's political capital is Yamoussoukro in the centre of the country, while its economic capital and largest city is the port city of Abidjan, it borders Guinea and Liberia to the west, Burkina Faso and Mali to the north, Ghana to the east, the Gulf of Guinea to the south. Before its colonization by Europeans, Ivory Coast was home to several states, including Gyaaman, the Kong Empire, Baoulé; the area became a protectorate of France in 1843 and was consolidated as a French colony in 1893 amid the European scramble for Africa. It achieved independence in 1960, led by Félix Houphouët-Boigny, who ruled the country until 1993. Stable by regional standards, Ivory Coast established close political and economic ties with its West African neighbors while at the same time maintaining close relations to the West France. Ivory Coast experienced a coup d'état in 1999 and two religiously-grounded civil wars, first between 2002 and 2007 and again during 2010–2011.
In 2000, the country adopted a new constitution. Ivory Coast is a republic with strong executive power vested in its president. Through the production of coffee and cocoa, the country was an economic powerhouse in West Africa during the 1960s and 1970s, though it went through an economic crisis in the 1980s, contributing to a period of political and social turmoil. Only around 2014 has GDP per capita in the country again reached the level of its peak in the 1970s. In the 21st century, the Ivorian economy is market-based and still relies on agriculture, with smallholder cash-crop production being dominant; the official language is French, with local indigenous languages widely used, including Baoulé, Dan and Cebaara Senufo. In total there are around 78 languages spoken in Ivory Coast. There are large populations of Muslims and various indigenous religions. Portuguese and French merchant-explorers in the 15th and 16th centuries divided the west coast of Africa roughly, into four "coasts" reflecting local economies.
The coast that the French named the Côte d'Ivoire and the Portuguese named the Costa Do Marfim—both mean "Coast of Ivory"—lay between what was known as the Guiné de Cabo Verde, so-called "Upper Guinea" at Cap-Vert, Lower Guinea. There was a Pepper Coast known as the "Grain Coast", a "Gold Coast", a "Slave Coast". Like those, the name "Ivory Coast" reflected the major trade that occurred on that particular stretch of the coast: the export of ivory. Other names included the Côte de Dents "Coast of Teeth", again reflecting the trade in ivory. One can find the name Cote de Dents used in older works, it was used in Duckett's Dictionnaire and by Nicolas Villault de Bellefond, for example, although Antoine François Prévost used Côte d'Ivoire. In the 19th century, usage switched to Côte d'Ivoire; the coastline of the modern state is not quite coterminous with what the 15th- and 16th-century merchants knew as the "Teeth" or "Ivory" coast, considered to stretch from Cape Palmas to Cape Three Points and, thus now divided between the modern states of Ghana and Ivory Coast.
It retained the name through French rule and independence in 1960. The name had long since been translated into other languages, which the post-independence government considered troublesome whenever its international dealings extended beyond the Francophone sphere. Therefore, in April 1986, the government declared that Côte d'Ivoire would be its formal name for the purposes of diplomatic protocol, since officially refuses to recognize or accept any translation from French to another language in its international dealings. Despite the Ivorian government's request, the English translation "Ivory Coast" is still used in English by various media outlets and publications; the first human presence in Ivory Coast has been difficult to determine because human remains have not been well preserved in the country's humid climate. However, newly found weapon and tool fragments have been interpreted as a possible indication of a large human presence during the Upper Paleolithic period, or at the minimum, the Neolithic period.
The earliest known inhabitants of Ivory Coast have left traces scattered throughout the territory. Historians believe that they were all either displaced or absorbed by the ancestors of the present indigenous inhabitants, who migrated south into the area before the 16th century; such groups included the Kotrowou, Zéhiri, Ega and Diès. The first recorded history appears in the chronicles of North African traders, from early Roman times, conducted a caravan trade across the Sahara in salt, slaves and other goods; the southern terminals of the trans-Saharan trade routes were located on the edge of the desert, from there supplemental trade extended as far south as the edge of the rain forest. The more important terminals—Djenné, Timbuctu—grew into major commercial centres around which the great Sudanic empires developed. By controlling the trade routes with their powerful military forces, these empires were able
Ethnologue: Languages of the World is an annual reference publication in print and online that provides statistics and other information on the living languages of the world. It was first issued in 1951, is now published annually by SIL International, a U. S.-based, Christian non-profit organization. SIL's main purpose is to study and document languages to promote literacy and for religious purposes; as of 2018, Ethnologue contains web-based information on 7,097 languages in its 21st edition, including the number of speakers, dialects, linguistic affiliations, availability of the Bible in each language and dialect described, a cursory description of revitalization efforts where reported, an estimate of language viability using the Expanded Graded Intergenerational Disruption Scale. Ethnologue has been published by SIL International, a Christian linguistic service organization with an international office in Dallas, Texas; the organization studies numerous minority languages to facilitate language development, to work with speakers of such language communities in translating portions of the Bible into their languages.
The determination of what characteristics define a single language depends upon sociolinguistic evaluation by various scholars. Ethnologue follows general linguistic criteria, which are based on mutual intelligibility. Shared language intelligibility features are complex, include etymological and grammatical evidence, agreed upon by experts. In addition to choosing a primary name for a language, Ethnologue provides listings of other name for the language and any dialects that are used by its speakers, government and neighbors. Included are any names that have been referenced regardless of whether a name is considered official, politically correct or offensive; these lists of names are not complete. In 1984, Ethnologue released a three-letter coding system, called an'SIL code', to identify each language that it described; this set of codes exceeded the scope of other standards, e.g. ISO 639-1 and ISO 639-2; the 14th edition, published in 2000, included 7,148 language codes. In 2002, Ethnologue was asked to work with the International Organization for Standardization to integrate its codes into a draft international standard.
The 15th edition of Ethnologue was the first edition to use this standard, called ISO 639-3. This standard is now administered separately from Ethnologue. In only one case and the ISO standards treat languages differently. ISO 639-3 considers Akan to be a macrolanguage consisting of two distinct languages and Fante, whereas Ethnologue considers Twi and Fante to be dialects of a single language, since they are mutually intelligible; this anomaly resulted because the ISO 639-2 standard has separate codes for Twi and Fante, which have separate literary traditions, all 639-2 codes for individual languages are automatically part of 639–3 though 639-3 would not assign them separate codes. In 2014, with the 17th edition, Ethnologue introduced a numerical code for language status using a framework called EGIDS, an elaboration of Fishman's GIDS, it ranks a language from 0 for an international language to 10 for an extinct language, i.e. a language with which no-one retains a sense of ethnic identity.
In December 2015, Ethnologue launched a metered paywall. As of 2017, Ethnologue's 20th edition described 237 language families including 86 language isolates and six typological categories, namely sign languages, pidgins, mixed languages, constructed languages, as yet unclassified languages. In 1986, William Bright editor of the journal Language, wrote of Ethnologue that it "is indispensable for any reference shelf on the languages of the world". In 2008 in the same journal, Lyle Campbell and Verónica Grondona said: "Ethnologue...has become the standard reference, its usefulness is hard to overestimate."In 2015, Harald Hammarström, an editor of Glottolog, criticized the publication for lacking citations and failing to articulate clear principles of language classification and identification. However, he concluded that, on balance, "Ethnologue is an impressively comprehensive catalogue of world languages, it is far superior to anything else produced prior to 2009." Starting with the 17th edition, Ethnologue has been published every year.
Linguasphere Observatory Register Lists of languages List of language families Martin Everaert. The Use of Databases in Cross-Linguistic Studies. Walter de Gruyter. ISBN 9783110198744. Retrieved 2014-07-13. Skutnabb-Kangas, Tove. Linguistic Genocide in Education-or Worldwide Diversity and Human Rights?. Routledge. ISBN 9781135662356. Retrieved 2014-07-13. Paolillo, John C.. "Evaluating language statistics: the Ethnologue and beyond". UNESCO Institute of Statistics. Pp. 3–5. Retrieved October 8, 2015. Web version of Ethnologue
Advanced and retracted tongue root
In phonetics, advanced tongue root and retracted tongue root, abbreviated ATR or RTR, are contrasting states of the root of the tongue during the pronunciation of vowels in some languages in Western and Eastern Africa but in Kazakh and Mongolian. ATR vs RTR used to be suggested to be the basis for the distinction between tense and lax vowels in European languages such as German, but that no longer seems tenable. Advanced tongue root, abbreviated ATR or +ATR called expanded, involves the expansion of the pharyngeal cavity by moving the base of the tongue forward and lowering the larynx during the pronunciation of a vowel; the lowering of the larynx sometimes adds a breathy quality to the vowel. Voiced stops such as, can involve non-contrastive tongue root advancement whose results can be seen in sound changes relating stop voicing and vowel frontness such as voicing stop consonants before front vowels in the Oghuz Turkic languages or in Adjarian's law: the fronting of vowels after voiced stops in certain dialects of Armenian.
True uvular consonants appear to be incompatible with advanced tongue root, i.e. they are inherently. Combined with the above tendency for voiced stops to be, that motivates the extreme rarity of the voiced uvular stop compared to its voiceless counterpart; the International Phonetic Alphabet represents ATR with a "left tack" diacritic. In languages in which they occur, advanced-tongue-root vowels often contrast with retracted tongue root vowels in a system of vowel harmony, which occurs in large parts of West and East Africa. ATR vowels involve a certain tension in the tongue in the lips and jaw as well. Nonetheless, phoneticians do not refer to ATR vowels as tense vowels since the word tense has several meanings in European phonetics. Retracted tongue root, abbreviated RTR, is the retraction of the base of the tongue in the pharynx during the pronunciation of a vowel, the opposite articulation of advanced tongue root, it is in effect partial pharyngealization, but it may contrast with full pharyngealization.
The neutral position of the tongue during the pronunciation of a vowel, contrasting with advanced tongue root and thus marked -ATR, is sometimes referred to as retracted tongue root. The diacritic for RTR in the International Phonetic Alphabet is the right tack. RTR vowels are called "lax", but it is not consistent between languages or between vowels in the same language; as mentioned above, many African languages, such as Maasai, have systems of vowel harmony based on tongue root position. That is illustrated here with the Fante dialect of Akan, which has fifteen vowels: five +ATR vowels, five −ATR vowels, five nasal vowels. There are two harmonization rules that govern the vowels that may co-occur in a word: All −ATR vowels become +ATR when followed by a peripheral +ATR vowel; that is, orthographic e ɛ a ɔ o become i e a o u before i u and sometimes before a. As long as it does not conflict with the previous rule, the +ATR mid vowels become −ATR high vowels when preceded by a −ATR non-high vowel.
In the Twi language, the ±ATR distinction has merged in the low vowel and so /a/ is harmonically neutral, occurring with either set of vowels. In addition, the two vowels written e and o are not distinguished and are equivalent to European and, as reflected in the orthography. With advances in fiber-optic laryngoscopy at the end of the twentieth century, new types of phonation were discovered that involve more of the larynx than just the glottis. One of the few languages studied thus far, the Togolese language Kabiyé, has a vocalic distinction, assumed to be one of tongue root. However, it turned out to be a phonation distinction of faucalized voice versus harsh voice, it is not yet clear whether, characteristic of ±ATR distinctions in general. The back-vowel constraint, an effect of tongue-root retraction in some click consonants
Airstream is an American brand of travel trailers which are recognized by the distinctive shape of their rounded and polished aluminum coachwork. This body shape dates back to the 1930s and is based on designs created by Hawley Bowlus, who had earlier overseen construction of Charles Lindbergh's aircraft, the Spirit of St. Louis. Airstream trailers and recreational vehicles are manufactured in Jackson Center, Ohio, USA; the company, now a division of Thor Industries, employs more than 800 people, is the oldest in the industry. The company was created by Wally Byam who began building trailers out of Masonite in his backyard in Los Angeles during the late 1920s. Byam published a magazine selling "how-to" kits to customers wishing to build their own trailers. In 1936, Byam introduced the "Airstream Clipper", a rebadged 1935 Bowlus, with the door relocated from the front to the side; the design thus improved fuel efficiency. It was the first of the now familiar sausage-shaped, silver aluminum Airstream trailers.
The first Airstream, called the "Clipper" in 1936, was named after the first trans-Atlantic seaplane. It slept four, carried its own water supply, was fitted with electric lights and cost $1,200. Of more than 400 travel trailer builders operating in 1936, Airstream was the sole survivor of the Depression. During World War II, travel became a luxury most could not afford and non-military industries faced an acute aluminum shortage; when World War II ended, the economy boomed, people's attention once again turned towards leisure travel. Byam's company went back into production in 1948. In July 1952, a new facility in Jackson Center, was established. 1979 saw the last Airstreams to be manufactured in California. In 1974, Airstream began manufacturing a Class A motorhome, badged "Argosy", they began as painted 20- and 24-foot models, were followed in 1979 by the first examples of the Classic model motorhome, with an unpainted aluminum body much like the trailers. Airstream-badged Class A motorhomes began as 24- and 28-foot models in 1979, in the 1980s and 1990s, models ranging from 25 up to 37 feet were marketed.
The aluminum motorhomes were followed by more traditional-looking fiberglass models in the 1990s. Airstream discontinued manufacture of Class A motorhomes in 2006. One bus model, the Skydeck, featured interior stairs leading to a deck on the roof. In 1981, Airstream's Commercial Vehicle Division marketed a Class A motorhome as a funeral coach, it was designed to transport family and the deceased from the funeral home to the cemetery. Starting in 1989, Airstream built Class B motorhomes based on the Ford Econoline chassis and the Dodge B-series van chassis. Production ceased after the 1999 model year. In 2004, Airstream introduced the Westfalia and Interstate, built on the Mercedes-Benz Sprinter chassis; the Westfalia was discontinued in 2006. Airstream, still based in Jackson Center, is a division of Inc.. Airstream produces several models — Basecamp, Flying Cloud, International Signature and Serenity, Tommy Bahama, Classic. 2016 trailer sizes range between 16 ft to 33 ft. Airstream are distributed across the UK from the Swift Group with three models made for the British market.
The Airstream Missouri and Colorado have been created with smaller dimensions to accommodate narrower European roads. The furniture and cabinetry in these models are still manufacturers as the HQ in Ohio and shipped over for each trailer. Airstream are popular amongst the European market for takeaway diners and business stands; as of January 2015 Airstream was producing about 2,600 per year. The company was expanding its capacity with plans to increase production by at least 50% over 2014 levels. By April 2016, the Dayton Business Journal reported Airstream was producing 72 trailers per week--an annual rate of 3,744 assuming consistent production all year; the same article said they were aiming to increase to 77 trailers per week in 2016. In 2016 Airstream acquired Nest Caravans, an Oregon-based company which had one product in development, at the prototype stage. Nest trailers are made of molded fiberglass; the Nest is a smaller and lower priced trailer than any in the Airstream line, but at the upper end of prices for its market segment, to be sold for $29,995 before the acquisition.
Airstream CEO Bob Wheeler said "Nest is a product that conveys sophistication and upscale modernity, so it made sense for us to partner and help bring this design to market." Airstream moved the company to Ohio and expanded staff for production, underway. Airstream Nest trailers are scheduled to be available in early 2018. There are more than a dozen Airstream parks throughout the United States; these are RV resorts or campgrounds where owners of Airstream-manufactured units are allowed to buy, rent or lease a site. Some of these facilities welcome non-Airstream products, while others are more strict in their admission; some of the parks require membership in the WBCCI to be admitted. Several of the resorts are owned and operated by the local unit of the WBCCI. Airstreamers are a group of "RV-ers" who share a community spirit because of their common love of the trailers. In the early 1950s, Airstream company founder Wally Byam began leading groups of owners on travels to many portions of the world, where the towed trailers were quite remarkable.
Photos taken of the trailers in front of many famous tourist sites were common. This promoted a mystique which surrounded persists to this day; the Wally Byam Caravan Club was formed during the 1955 rally in Nova Scotia, Canada. The word "International" wa
International Phonetic Alphabet
The International Phonetic Alphabet is an alphabetic system of phonetic notation based on the Latin alphabet. It was devised by the International Phonetic Association in the late 19th century as a standardized representation of the sounds of spoken language; the IPA is used by lexicographers, foreign language students and teachers, speech-language pathologists, actors, constructed language creators and translators. The IPA is designed to represent only those qualities of speech that are part of oral language: phones, phonemes and the separation of words and syllables. To represent additional qualities of speech, such as tooth gnashing and sounds made with a cleft lip and cleft palate, an extended set of symbols, the extensions to the International Phonetic Alphabet, may be used. IPA symbols are composed of one or more elements of two basic types and diacritics. For example, the sound of the English letter ⟨t⟩ may be transcribed in IPA with a single letter, or with a letter plus diacritics, depending on how precise one wishes to be.
Slashes are used to signal broad or phonemic transcription. Letters or diacritics are added, removed or modified by the International Phonetic Association; as of the most recent change in 2005, there are 107 letters, 52 diacritics and four prosodic marks in the IPA. These are shown in the current IPA chart, posted below in this article and at the website of the IPA. In 1886, a group of French and British language teachers, led by the French linguist Paul Passy, formed what would come to be known from 1897 onwards as the International Phonetic Association, their original alphabet was based on a spelling reform for English known as the Romic alphabet, but in order to make it usable for other languages, the values of the symbols were allowed to vary from language to language. For example, the sound was represented with the letter ⟨c⟩ in English, but with the digraph ⟨ch⟩ in French. However, in 1888, the alphabet was revised so as to be uniform across languages, thus providing the base for all future revisions.
The idea of making the IPA was first suggested by Otto Jespersen in a letter to Paul Passy. It was developed by Alexander John Ellis, Henry Sweet, Daniel Jones, Passy. Since its creation, the IPA has undergone a number of revisions. After revisions and expansions from the 1890s to the 1940s, the IPA remained unchanged until the Kiel Convention in 1989. A minor revision took place in 1993 with the addition of four letters for mid central vowels and the removal of letters for voiceless implosives; the alphabet was last revised in May 2005 with the addition of a letter for a labiodental flap. Apart from the addition and removal of symbols, changes to the IPA have consisted of renaming symbols and categories and in modifying typefaces. Extensions to the International Phonetic Alphabet for speech pathology were created in 1990 and adopted by the International Clinical Phonetics and Linguistics Association in 1994; the general principle of the IPA is to provide one letter for each distinctive sound, although this practice is not followed if the sound itself is complex.
This means that: It does not use combinations of letters to represent single sounds, the way English does with ⟨sh⟩, ⟨th⟩ and ⟨ng⟩, or single letters to represent multiple sounds the way ⟨x⟩ represents /ks/ or /ɡz/ in English. There are no letters that have context-dependent sound values, as do "hard" and "soft" ⟨c⟩ or ⟨g⟩ in several European languages; the IPA does not have separate letters for two sounds if no known language makes a distinction between them, a property known as "selectiveness". Among the symbols of the IPA, 107 letters represent consonants and vowels, 31 diacritics are used to modify these, 19 additional signs indicate suprasegmental qualities such as length, tone and intonation; these are organized into a chart. The letters chosen for the IPA are meant to harmonize with the Latin alphabet. For this reason, most letters modifications thereof; some letters are neither: for example, the letter denoting the glottal stop, ⟨ʔ⟩, has the form of a dotless question mark, derives from an apostrophe.
A few letters, such as that of the voiced pharyngeal fricative, ⟨ʕ⟩, were inspired by other writing systems. Despite its preference for harmonizing with the Latin script, the International Phonetic Association has admitted other letters. For example, before 1989, the IPA letters for click consonants were ⟨ʘ⟩, ⟨ʇ⟩, ⟨ʗ⟩, ⟨ʖ⟩, all of which were derived either from existing IPA letters, or from Latin and Greek letters. However, except for ⟨ʘ⟩, none of these letters were used among Khoisanists or Bantuists, as a result they were replaced by the more widespread symbols ⟨ʘ⟩, ⟨ǀ⟩, ⟨ǃ⟩, ⟨ǂ⟩, ⟨ǁ⟩ at the IPA Kiel Convention in 1989. Although the IPA diacritics are featural, there is little systemicity in the letter forms. A retroflex articulation is indicated with a right-swinging tail, as in ⟨ɖ ʂ ɳ⟩, implosion by a top hook, ⟨ɓ ɗ ɠ⟩, but other pseudo-featural elements are due to haphazard derivation and coincidence. For example, all nasal consonants but uvular ⟨ɴ⟩ are based on the form ⟨n⟩: ⟨m ɱ n ɳ ɲ ŋ⟩.
However, the similarity between ⟨m⟩ and ⟨n⟩ is a historical accident. Some of the new letters were ordinary Latin letters tu
The term phonation has 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, 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; the phonatory process, or voicing, occurs when air is expelled from the lungs through the glottis, creating a pressure drop across the larynx. When this drop becomes sufficiently large, the vocal folds start to oscillate; the minimum pressure drop required to achieve phonation is called the phonation threshold pressure, for humans with normal vocal folds, it is 2–3 cm H2O.
The motion of the vocal folds during oscillation is lateral, though there is some superior component as well. However, there is no motion along the length of the vocal folds; the oscillation of the vocal folds serves to modulate the pressure and flow of the air through the larynx, this modulated airflow is the main component of the sound of most voiced phones. The sound that the larynx produces is a harmonic series. In other words, it consists of a fundamental tone accompanied by harmonic overtones, which are multiples of the fundamental frequency. According to the source–filter theory, the resulting sound excites the resonance chamber, the vocal tract to produce the individual speech sounds; the vocal folds will not oscillate if they are not sufficiently close to one another, are not under sufficient tension or under too much tension, or if the pressure drop across the larynx is not sufficiently large. In linguistics, a phone is called voiceless. In speech, voiceless phones are associated with vocal folds that are elongated tensed, placed laterally when compared to vocal folds during phonation.
Fundamental frequency, the main acoustic cue for the percept pitch, can be varied through a variety of means. Large scale changes are accomplished by increasing the tension in the vocal folds through contraction of the cricothyroid muscle. Smaller changes in tension can be effected by contraction of the thyroarytenoid muscle or changes in the relative position of the thyroid and cricoid cartilages, as may occur when the larynx is lowered or raised, either volitionally or through movement of the tongue to which the larynx is attached via the hyoid bone. In addition to tension changes, fundamental frequency is affected by the pressure drop across the larynx, affected by the pressure in the lungs, will vary with the distance between the vocal folds. Variation in fundamental frequency is used linguistically to produce tone. There are two main theories as to how vibration of the vocal folds is initiated: the myoelastic theory and the aerodynamic theory; these two theories are not in contention with one another and it is quite possible that both theories are true and operating to initiate and maintain vibration.
A third theory, the neurochronaxic theory, was in considerable vogue in the 1950s, but has since been discredited. The myoelastic theory states that when the vocal cords are brought together and breath pressure is applied to them, the cords remain closed until the pressure beneath them, the subglottic pressure, is sufficient to push them apart, allowing air to escape and reducing the pressure enough for the muscle tension recoil to pull the folds back together again; the pressure builds up once again until the cords are pushed apart, the whole cycle keeps repeating itself. The rate at which the cords open and close, the number of cycles per second, determines the pitch of the phonation; the aerodynamic theory is based on the Bernoulli energy law in fluids. The theory states that when a stream of breath is flowing through the glottis while the arytenoid cartilages are held together, a push-pull effect is created on the vocal fold tissues that maintains self-sustained oscillation; the push occurs during glottal opening, when the glottis is convergent, the pull occurs during glottal closing, when the glottis is divergent.
Such an effect causes a transfer of energy from the airflow to the vocal fold tissues which overcomes losses by dissipation and sustain the oscillation. The amount of lung pressure needed to begin phonation is defined by Titze as the oscillation threshold pressure. During glottal closure, the air flow is cut off until breath pressure pushes the folds apart and the flow starts up again, causing the cycles to repeat; the textbook entitled Myoelastic Aerodynamic Theory of Phonation by Ingo Titze credits Janwillem van den Berg as the originator of the theory and provides detailed mathematical development of the theory. This theory states that the frequency of the vocal fold vibration is determined by the chronaxie of the recurrent nerve, not by breath pressure or muscular tension. Advocates of this theory thought that every single vibration of the vocal folds was due to an impulse from the recurrent laryngeal nerves and that the acoustic center in the brain regulated the speed of vocal fold vibration.
Speech and voice scientists have long since left this theory as the muscles have been shown to not be able to contract fast enough to accomplish the vibration. In addition, persons with paralyzed vocal folds can produce phonation, whic