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Articulatory phonetics studies how the moving structures of the vocal tract produce speech. Airflow supplies energy; vocal fold vibration can provide a repeating source; the tongue, lips and other articulators shape or interrupt the flow. Producing voice and shaping recognizable speech are related but distinguishable processes.^[ref]

A simple observation compares a sustained “mmm” with a sustained “sss”. Lightly touching the outside of the throat can help detect the vibration accompanying voicing, while a mirror shows the different lip configurations. This is a qualitative demonstration: the external sensation alone does not measure the detailed motion of the vocal folds.

Descriptions of consonants commonly distinguish place of articulation, where a constriction is formed, from manner of articulation, how the airflow is modified. These descriptions explain why changing the tongue or lips can change the recorded sound without changing the source of airflow. Acoustic phonetics measures the resulting signal, while articulation describes its physical production.

A bilabial consonant uses the two lips to form its principal constriction. The term specifies place of articulation; it leaves manner of articulation and voicing to be stated separately. The lower lip approaches the upper lip rather than the upper teeth.^[ref]

The sounds [p], [b] and [m] share a bilabial closure. The first two are oral stops, while [m] permits nasal airflow; their shared lip position therefore does not determine whether sustained sound is possible during closure. A mirror provides direct evidence of the lip configuration, but it cannot alone establish the state of the vocal folds or the soft palate.

A lip is a movable fold at the entrance to the mouth, with skin externally and oral mucosa internally. The lips contain the orbicularis oris muscle, whose contraction helps close and shape the oral opening. Their sensory supply helps guide contact with food and objects.^[ref]

The oral seal has several functions. During eating it helps retain food; during speech, closure and release can interrupt airflow, while rounding changes the geometry of the vocal tract. A bilabial stop such as /p/ uses contact between both lips, whereas a rounded vowel uses an open but reshaped outlet. The visible fold and the muscle controlling it are related structures, rather than identical anatomical objects.

The mouth is the entrance to the digestive tract and a movable part of the vocal tract. Its cavity is bounded by the lips, cheeks, palate and floor of the mouth, with the tongue occupying much of the space. The teeth break food into smaller pieces while the tongue and cheeks position it for chewing and swallowing.^[ref]

Mechanical processing and chemical processing cooperate: mixing food with saliva makes a movable bolus and exposes it to salivary components. The same cavity also changes shape during speech. Opening the jaw or repositioning the tongue changes the passage through which air and sound travel, so digestive anatomy is also an articulatory instrument.

A nasal consonant combines a constriction or closure in the mouth with an open airflow route through the nose. Lowering the soft palate opens that route; the mouth can remain closed at the consonant's place of articulation. A sustained [m] therefore produces sound despite closed lips, whereas closing both routes stops sustained outward flow.^[ref]

Compare [m], [n] and [ŋ]. They share a nasal manner of articulation, while their oral closures occupy different places. Comparing [m] with [b] instead holds the bilabial closure approximately fixed while changing the available airflow route. Voicing and the resonant vocal tract shape the recorded signal; the written letter alone does not specify those physical properties.

The orbicularis oris muscle is a complex of skeletal muscle fibres around the mouth that closes and shapes the lips. Its contraction can press the lips together or project them forward. Compare sealing the mouth while holding water with rounding the lips to whistle: both use the same muscular region to change the outlet's shape. The visible lip includes other tissues besides the muscle that moves it.^[ref]

Phonetics studies the physical production, transmission and perception of speech. Articulatory phonetics examines the moving structures that shape the airflow; acoustic phonetics examines the resulting sound waves; auditory phonetics examines how a listener perceives them. These are different measurements along the same communication chain.

During voiced speech, airflow from the lungs drives vocal fold vibration. Movements of the tongue, lips and other parts of the vocal tract shape the emerging sound. This separates the production of a vibrating source from the articulation of recognizable speech, and both from the language expressed by it.^[ref]

A simple acoustic comparison records the same spoken phrase twice, once as a statement and once as a question. The sound pressure time series and its spectrogram allow changes in fundamental frequency, segment duration and pauses to be compared. The comparison investigates physical differences in prosody; the written words alone do not specify those measurements.

The vocal tract is the air passage above the sound-producing region of the larynx, including the pharyngeal, oral and, when acoustically coupled, nasal cavities. Movements of the tongue, lips, jaw and soft palate change its shape. These changes help turn a laryngeal sound source or a turbulent air stream into distinguishable speech sounds.^[ref]

A simple acoustic model treats an unbranched tract of length $L$ as a uniform tube closed at one end and open at the other. A pressure maximum at the closed end and pressure minimum at the open end allow odd quarter wavelengths, givingWith $L=0.17$ m and sound speed $c=340$ m/s, these resonances are $500$, $1500$ and $2500$ Hz. A real vocal tract is neither uniform nor permanently closed at the glottis; its varying cross-section and branching shift the resonances. These spectral resonances, associated with formants, differ from the repetition frequency of vocal-fold vibration. This is why changing articulation can change a vowel without requiring the same change in voice pitch.