Editing Phonetics (section)

== Acoustics ==
[[File:Waveform spectrogram and transcription of wikipedia in praat.png|thumb|upright=1.5|A waveform (top), spectrogram (middle), and transcription (bottom) of a woman saying "Wikipedia" displayed using the [[Praat]] software for linguistic analysis {{listen
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Speech sounds are created by the modification of an airstream which results in a sound wave. The modification is done by the articulators, with different places and manners of articulation producing different acoustic results. Because the posture of the vocal tract, not just the position of the tongue can affect the resulting sound, the [[manner of articulation]] is important for describing the speech sound. The words ''tack'' and ''sack'' both begin with alveolar sounds in English, but differ in how far the tongue is from the alveolar ridge. This difference has large effects on the air stream and thus the sound that is produced. Similarly, the direction and source of the airstream can affect the sound. The most common airstream mechanism is pulmonic—using the lungs—but the glottis and tongue can also be used to produce airstreams.

===Voicing and phonation types===
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A major distinction between speech sounds is whether they are voiced. Sounds are voiced when the vocal folds begin to vibrate in the process of phonation. Many sounds can be produced with or without phonation, though physical constraints may make phonation difficult or impossible for some articulations. When articulations are voiced, the main source of noise is the periodic vibration of the vocal folds. Articulations like voiceless plosives have no acoustic source and are noticeable by their silence, but other voiceless sounds like fricatives create their own acoustic source regardless of phonation.

Phonation is controlled by the muscles of the larynx, and languages make use of more acoustic detail than binary voicing. During phonation, the vocal folds vibrate at a certain rate. This vibration results in a periodic acoustic waveform comprising a [[fundamental frequency]] and its harmonics. The fundamental frequency of the acoustic wave can be controlled by adjusting the muscles of the larynx, and listeners perceive this fundamental frequency as pitch. Languages use pitch manipulation to convey lexical information in tonal languages, and many languages use pitch to mark prosodic or pragmatic information.

For the vocal folds to vibrate, they must be in the proper position and there must be air flowing through the glottis.{{sfn|Ohala|1997|p=1}} Phonation types are modeled on a continuum of glottal states from completely open (voiceless) to completely closed (glottal stop). The optimal position for vibration, and the phonation type most used in speech, modal voice, exists in the middle of these two extremes. If the glottis is slightly wider, breathy voice occurs, while bringing the vocal folds closer together results in creaky voice.{{sfn|Gordon|Ladefoged|2001}}

The normal phonation pattern used in typical speech is modal voice, where the vocal folds are held close together with moderate tension. The vocal folds vibrate as a single unit periodically and efficiently with a full glottal closure and no aspiration.{{Sfn|Gobl|Ní Chasaide|2010|p=399}} If they are pulled farther apart, they do not vibrate and so produce voiceless phones. If they are held firmly together they produce a glottal stop.{{sfn|Gordon|Ladefoged|2001}}<!--I think, double check-->

If the vocal folds are held slightly further apart than in modal voicing, they produce phonation types like breathy voice (or murmur) and whispery voice. The tension across the vocal ligaments ([[vocal cords]]) is less than in modal voicing allowing for air to flow more freely. Both breathy voice and whispery voice exist on a continuum loosely characterized as going from the more periodic waveform of breathy voice to the more noisy waveform of whispery voice. Acoustically, both tend to dampen the first formant with whispery voice showing more extreme deviations.{{Sfn|Gobl|Ní Chasaide|2010|p=400-401}}

Holding the vocal folds more tightly together results in a creaky voice. The tension across the vocal folds is less than in modal voice, but they are held tightly together resulting in only the ligaments of the vocal folds vibrating.{{efn|See [[#The larynx]] for further information on the anatomy of phonation.}} The pulses are highly irregular, with low pitch and frequency amplitude.{{sfn|Gobl|Ní Chasaide|2010|p=401}}
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Some languages do not maintain a voicing distinction for some consonants,{{efn|Hawaiian, for example, does not contrast voiced and voiceless plosives.}} but all languages use voicing to some degree. For example, no language is known to have a phonemic voicing contrast for vowels with all known vowels canonically voiced.{{efn|There are languages, like [[Japanese language|Japanese]], where vowels are produced as voiceless in certain contexts.}} Other positions of the glottis, such as breathy and creaky voice, are used in a number of languages, like [[Jalapa Mazatec]], to contrast [[phonemes]] while in other languages, like English, they exist allophonically.

There are several ways to determine if a segment is voiced or not, the simplest being to feel the larynx during speech and note when vibrations are felt. More precise measurements can be obtained through acoustic analysis of a spectrogram or spectral slice. In a spectrographic analysis, voiced segments show a voicing bar, a region of high acoustic energy, in the low frequencies of voiced segments.{{sfn|Dawson|Phelan|2016}} In examining a spectral splice, the acoustic spectrum at a given point in time a model of the vowel pronounced reverses the filtering of the mouth producing the spectrum of the glottis. A computational model of the unfiltered glottal signal is then fitted to the inverse filtered acoustic signal to determine the characteristics of the glottis.{{sfn|Gobl|Ní Chasaide|2010|pp=388, ''et seq''}} Visual analysis is also available using specialized medical equipment such as ultrasound and endoscopy.{{sfn|Dawson|Phelan|2016}}{{efn|See [[#Articulatory models]] for further information on acoustic modeling.}}

=== Vowels ===
{{IPA vowels|class=floatright}}
Vowels are broadly categorized by the area of the mouth in which they are produced, but because they are produced without a constriction in the vocal tract their precise description relies on measuring acoustic correlates of tongue position. The location of the tongue during vowel production changes the frequencies at which the cavity resonates, and it is these resonances—known as [[formants]]—which are measured and used to characterize vowels.

Vowel height traditionally refers to the highest point of the tongue during articulation.{{Sfn|Ladefoged|Maddieson|1996|p=282}} The height parameter is divided into four primary levels: high (close), close-mid, open-mid, and low (open). Vowels whose height are in the middle are referred to as mid. Slightly opened close vowels and slightly closed open vowels are referred to as near-close and near-open respectively. The lowest vowels are not just articulated with a lowered tongue, but also by lowering the jaw.{{Sfn|Lodge|2009|p=39}}

While the IPA implies that there are seven levels of vowel height, it is unlikely that a given language can minimally contrast all seven levels. [[Chomsky]] and [[Morris Halle|Halle]] suggest that there are only three levels,{{Sfn|Chomsky|Halle|1968|p=}} although four levels of vowel height seem to be needed to describe [[Danish language|Danish]] and it is possible that some languages might even need five.{{Sfn|Ladefoged|Maddieson|1996|p=289}}

Vowel backness is dividing into three levels: front, central and back. Languages usually do not minimally contrast more than two levels of vowel backness. Some languages claimed to have a three-way backness distinction include [[Nimboran]] and [[Norwegian language|Norwegian]].{{Sfn|Ladefoged|Maddieson|1996|p=290}}

In most languages, the lips during vowel production can be classified as either rounded or unrounded (spread), although other types of lip positions, such as compression and protrusion, have been described. Lip position is correlated with height and backness: front and low vowels tend to be unrounded whereas back and high vowels are usually rounded.{{Sfn|Ladefoged|Maddieson|1996|p=292-295}} Paired vowels on the IPA chart have the spread vowel on the left and the rounded vowel on the right.{{Sfn|Lodge|2009|p=40}}

Together with the universal vowel features described above, some languages have additional features such as [[Nasal vowel|nasality]], [[Vowel length|length]] and different types of phonation such as [[voiceless]] or [[Creaky voice|creaky]]. Sometimes more specialized tongue gestures such as [[Rhotic vowel|rhoticity]], [[advanced tongue root]], [[pharyngealization]], [[Strident vowel|stridency]] and frication are required to describe a certain vowel.{{Sfn|Ladefoged|Maddieson|1996|p=298}}

=== Manner of articulation ===
{{main|Manner of articulation}}
Knowing the place of articulation is not enough to fully describe a consonant, the way in which the stricture happens is equally important. Manners of articulation describe how exactly the active articulator modifies, narrows or closes off the vocal tract.{{Sfn|Ladefoged|Johnson|2011|p=14}}

[[Stop consonant|Stops]] (also referred to as plosives) are consonants where the airstream is completely obstructed. Pressure builds up in the mouth during the stricture, which is then released as a small burst of sound when the articulators move apart. The velum is raised so that air cannot flow through the nasal cavity. If the velum is lowered and allows for air to flow through the nose, the result in a nasal stop. However, phoneticians almost always refer to nasal stops as just "nasals".{{Sfn|Ladefoged|Johnson|2011|p=14}} [[Affricates]] are a sequence of stops followed by a fricative in the same place.{{Sfn|Ladefoged|Johnson|2011|p=67}}

[[Fricatives]] are consonants where the airstream is made turbulent by partially, but not completely, obstructing part of the vocal tract.{{Sfn|Ladefoged|Johnson|2011|p=14}} [[Sibilant]]s are a special type of fricative where the turbulent airstream is directed towards the teeth,{{Sfn|Ladefoged|Maddieson|1996|p=145}} creating a high-pitched hissing sound.{{Sfn|Ladefoged|Johnson|2011|p=15}}

[[Nasals]] (sometimes referred to as nasal stops) are consonants in which there's a closure in the oral cavity and the velum is lowered, allowing air to flow through the nose.{{Sfn|Ladefoged|Maddieson|1996|p=102}}

In an [[approximant]], the articulators come close together, but not to such an extent that allows a turbulent airstream.{{Sfn|Ladefoged|Johnson|2011|p=15}}

[[Lateral consonant|Laterals]] are consonants in which the airstream is obstructed along the center of the vocal tract, allowing the airstream to flow freely on one or both sides.{{Sfn|Ladefoged|Johnson|2011|p=15}} Laterals have also been defined as consonants in which the tongue is contracted in such a way that the airstream is greater around the sides than over the center of the tongue.{{Sfn|Ladefoged|Maddieson|1996|p=182}} The first definition does not allow for air to flow over the tongue.

[[Trill consonant|Trills]] are consonants in which the tongue or lips are set in motion by the airstream.{{Sfn|Ladefoged|Johnson|2011|p=175}} The stricture is formed in such a way that the airstream causes a repeating pattern of opening and closing of the soft articulator(s).{{Sfn|Ladefoged|Maddieson|1996|p=217}} Apical trills typically consist of two or three periods of vibration.{{Sfn|Ladefoged|Maddieson|1996|p=218}}

[[Flap consonant|Taps]] and [[Flap consonant|flaps]] are single, rapid, usually [[Apical consonant|apical]] gestures where the tongue is thrown against the roof of the mouth, comparable to a very rapid stop.{{Sfn|Ladefoged|Johnson|2011|p=175}} These terms are sometimes used interchangeably, but some phoneticians make a distinction.{{Sfn|Ladefoged|Maddieson|1996|p=230-231}} In a tap, the tongue contacts the roof in a single motion whereas in a flap the tongue moves tangentially to the roof of the mouth, striking it in passing.

During a [[glottalic airstream mechanism]], the glottis is closed, trapping a body of air. This allows for the remaining air in the vocal tract to be moved separately. An upward movement of the closed glottis will move this air out, resulting in it an [[ejective consonant]]. Alternatively, the glottis can lower, sucking more air into the mouth, which results in an [[implosive consonant]].{{Sfn|Ladefoged|Johnson|2011|p=137}}

[[Click consonant|Clicks]] are stops in which tongue movement causes air to be sucked in the mouth, this is referred to as a [[velaric airstream]].{{Sfn|Ladefoged|Maddieson|1996|p=78}} During the click, the air becomes [[rarefied]] between two articulatory closures, producing a loud 'click' sound when the anterior closure is released. The release of the anterior closure is referred to as the click influx. The release of the posterior closure, which can be velar or uvular, is the click efflux. Clicks are used in several African language families, such as the [[Khoisan languages|Khoisan]] and [[Bantu languages|Bantu]] languages.{{Sfn|Ladefoged|Maddieson|1996|p=246-247}}

===Pulmonary and subglottal system===
{{see|Breathing}}
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The lungs drive nearly all speech production, and their importance in phonetics is due to their creation of pressure for pulmonic sounds. The most common kinds of sound across languages are pulmonic egress, where air is exhaled from the lungs.{{sfn|Ladefoged|2001|p=1}} The opposite is possible, though no language is known to have pulmonic ingressive sounds as phonemes.{{sfn|Eklund|2008|p=237}} Many languages such as [[Swedish language|Swedish]] use them for [[paralinguistic]] articulations such as affirmations in a number of genetically and geographically diverse languages.{{sfn|Eklund|2008}} Both egressive and ingressive sounds rely on holding the vocal folds in a particular posture and using the lungs to draw air across the vocal folds so that they either vibrate (voiced) or do not vibrate (voiceless).{{sfn|Ladefoged|2001|p=1}} Pulmonic articulations are restricted by the volume of air able to be exhaled in a given respiratory cycle, known as the [[vital capacity]].

The lungs are used to maintain two kinds of pressure simultaneously to produce and modify phonation. To produce phonation at all, the lungs must maintain a pressure of 3–5&nbsp;cm H<sub>2</sub>O higher than the pressure above the glottis. However small and fast adjustments are made to the subglottal pressure to modify speech for suprasegmental features like stress. A number of thoracic muscles are used to make these adjustments. Because the lungs and thorax stretch during inhalation, the elastic forces of the lungs alone can produce pressure differentials sufficient for phonation at lung volumes above 50 percent of vital capacity.{{sfn|Seikel|Drumright|King|2016|p=176}} Above 50 percent of vital capacity, the [[respiratory muscles]] are used to "check" the elastic forces of the thorax to maintain a stable pressure differential. Below that volume, they are used to increase the subglottal pressure by actively exhaling air.

During speech, the respiratory cycle is modified to accommodate both linguistic and biological needs. Exhalation, usually about 60 percent of the respiratory cycle at rest, is increased to about 90 percent of the respiratory cycle. Because metabolic needs are relatively stable, the total volume of air moved in most cases of speech remains about the same as quiet tidal breathing.{{sfn|Seikel|Drumright|King|2016|p=171}} Increases in speech intensity of 18&nbsp;dB (a loud conversation) has relatively little impact on the volume of air moved. Because their respiratory systems are not as developed as adults, children tend to use a larger proportion of their vital capacity compared to adults, with more deep inhales.{{sfn|Seikel|Drumright|King|2016|pp=168–77}}

=== Source–filter theory ===
{{main|Source–filter model}}
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The source–filter model of speech is a theory of speech production which explains the link between vocal tract posture and the acoustic consequences. Under this model, the vocal tract can be modeled as a noise source coupled onto an [[acoustic filter]].{{sfn|Johnson|2008|p=83–5}} The noise source in many cases is the larynx during the process of voicing, though other noise sources can be modeled in the same way. The shape of the supraglottal vocal tract acts as the filter, and different configurations of the articulators result in different acoustic patterns. These changes are predictable. The vocal tract can be modeled as a sequence of tubes, closed at one end, with varying diameters, and by using equations for [[acoustic resonance]] the acoustic effect of an articulatory posture can be derived.{{sfn|Johnson|2008|p=104–5}} The process of inverse filtering uses this principle to analyze the source spectrum produced by the vocal folds during voicing. By taking the inverse of a predicted filter, the acoustic effect of the supraglottal vocal tract can be undone giving the acoustic spectrum produced by the vocal folds.{{sfn|Johnson|2008|p=157}} This allows quantitative study of the various phonation types.