Phonetics

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.

A consonant is a speech sound articulated with a closure or constriction that significantly shapes or interrupts airflow. Its physical description typically specifies place of articulation, manner of articulation and voicing. These describe where the articulators act, how the air passes and whether the vocal folds vibrate.^[ref]

The sounds [p] and [b] both involve the lips and a closure, but differ in their usual voicing classification. A sustained [m] also closes the lips, while opening a route through the nose: an oral closure does not imply that all airflow stops. The distinction between a plosive and a nasal consonant therefore depends on airflow paths, not merely the fact that two lips touch.

The category concerns speech sounds, rather than letters: a written symbol's name and its sound in a particular word are different objects of study. A consonant can also function as a syllabic consonant, so a syllable nucleus is not invariably a vowel.

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.

A vowel is a speech sound produced with a relatively open vocal tract, allowing its configuration to shape the sound without the complete closure or strong constriction characteristic of many consonants. Vowel height, vowel backness and lip rounding describe major articulatory differences. The vocal tract's acoustic resonances help determine the resulting formants.^[ref]

For example, [i] is a close front unrounded vowel, whereas [u] is close, back and rounded. Moving between them changes the tongue and lips, even if the fundamental frequency of vocal fold vibration is kept approximately constant. This separates vowel quality from pitch.

Many vowels occupy a syllable nucleus, but articulatory and syllabic descriptions answer different questions: a syllabic consonant can occupy that position too. Written vowel letters are also distinct from vowel sounds; the same spelling can correspond to different pronunciations.

A monophthong is a vowel with relatively stable quality through its central portion, in contrast with a diphthong's substantial movement between qualities. Relatively stable does not mean physically unchanging: neighboring sounds, vocal tract movement and the analysis interval can all affect a recording.^[ref]

For a stipulated acoustic illustration, hold the first two formants at $F_1=300$ and $F_2=2200$ hertz, while varying fundamental frequency from 100 to 150 hertz. The model changes voice pitch without requiring the same change in the formant pattern. Conversely, changing formants can change vowel quality while fundamental frequency stays fixed.

An experimental analysis can record a sustained vowel and compare several points within a consistently chosen interval. Changes concentrated near consonant boundaries need not make the whole segment a diphthong. The distinction therefore combines a phonetic trajectory with an analysis of the language's sound units.

A diphthong is a vowel whose quality changes during its production, conventionally treated as one dynamic vowel unit. A monophthong has relatively stable quality instead. The vowel in English toy, often transcribed [ɔɪ], moves from a back rounded quality toward a high front unrounded quality.^[ref]

A recording can represent that change through formant trajectories. For an invented illustration, let normalized vowel time be $0\le u\le 1$ and setin hertz. These are stipulated linear interpolation tracks, not measurements of toy. Their endpoints differ even if fundamental frequency stays fixed, separating changing vowel quality from voice pitch. Real trajectories need not be linear, and identifying a single diphthong rather than a sequence of separate vowels requires phonological evidence as well as an acoustic curve.

Vowel height describes the relatively high or low configuration of the tongue during a vowel, together with the corresponding openness of the mouth. Close or high vowels, such as [i], use a smaller opening than open or low vowels, such as [a]. The category describes articulation rather than perceived pitch.^[ref]

An observation exercise alternates sustained [i] and [a] while attempting to keep pitch steady. The jaw and tongue configuration change even when vocal fold repetition rate remains similar. Recording the formants and the fundamental frequency measures different aspects of this contrast. The labels high, mid and low divide a continuous articulatory space into useful regions; they are not universal distances in millimetres.

Vowel backness describes how far forward or backward the principal tongue constriction lies during a vowel. Front, central and back are broad regions of this articulatory continuum. It is a separate descriptive dimension from vowel height and lip rounding.^[ref]

The close vowels [i] and [u] give a familiar front/back contrast, but they also differ in ordinary lip rounding. Comparing them alone consequently does not isolate the effect of vowel backness. Holding another articulatory dimension approximately fixed, or measuring it separately, makes a stronger experiment. A vowel chart summarizes configurations; it is not a literal scale drawing of every speaker's vocal tract.

Lip rounding is the narrowing and reshaping of the lip opening, often with protrusion, used in producing some vowels. Rounded and unrounded configurations alter the acoustic filtering of the vocal tract. Lip rounding is distinct from vowel height and vowel backness, even though particular languages commonly associate these properties.^[ref]

Compare [i] with [y]: both are close front vowels, while [y] is rounded. A mirror makes the lip difference visible; a recording permits their formants to be compared. Keeping the intended tongue position and pitch similar helps separate the manipulation from simultaneous changes. The unrounded/rounded label is a concise category, while actual movements and the opening's geometry vary continuously.

Auditory phonetics investigates how listeners hear and interpret the physical sounds of speech. The input is an acoustic signal, but the outcome is a perceptual response: identifying a sound, discriminating two recordings or judging their similarity. It connects acoustic phonetics to hearing and to learned phonetic categories.

A simple controlled listening experiment presents pairs of recorded sounds in a randomized order and asks whether they differ. A separate identification task asks which category each recording belongs to. The tasks answer different questions: a listener can detect a physical difference without assigning the recordings to different phonemes. Praat supports forced-choice listening tasks, including same–different and AXB discrimination designs.^[ref]

The sound history presented to a listener can also matter. In Jessica Maye's infant study with collaborators, different exposure distributions along a speech-sound continuum produced different later discrimination patterns. The result concerns the tested exposure and task, rather than a complete account of how a language's sound system develops.^[ref]

Acoustic phonetics studies speech as a physical sound wave. A microphone records a signal related to changing sound pressure; analysis asks how its amplitude, timing and frequency content vary. A waveform displays variation over time, whereas a spectrogram displays the distribution of signal energy across both time and frequency.

For an original comparison, record a sustained vowel followed by a sustained hiss. Inspect each waveform at the same time scale and compare their spectrograms. Approximately repeated vocal cycles can give a harmonic structure, while the hiss provides an example of a noisier excitation. Broad spectral concentrations associated with the vocal tract are formants; they should be distinguished from the fundamental frequency of a repeating source. The spectrogram's analysis-window duration affects which temporal and spectral details are visible.^[ref]

These are measurements of the signal, rather than direct readings of a listener's perceived pitch or a speaker's tongue position. Relating the signal to perception and production requires auditory phonetics and articulatory phonetics.

A formant is a resonant spectral feature associated with the filtering of speech by the vocal tract. Its centre frequency and bandwidth describe different aspects of the feature; the first few formants are conventionally labeled $F_1,F_2,\dots$. Praat represents estimated formant structure as time-sampled centre frequencies and bandwidths.^[ref]

A simple physical model treats the vocal tract as a uniform tube, closed at one end and open at the other. Under those ideal boundary conditions its resonance frequencies arewhere $c$ is the speed of sound and $L$ the tube length. For $L=0.17\mathrm{m}$ and $c=340\mathrm{m}{\mathrm{s}}^{-1}$, the first three model resonances are 500, 1500 and 2500 hertz. A real vocal tract has a varying cross-section, losses and moving articulators, so this illustrates the mechanism rather than predicting every vowel.

These resonances are distinct from the fundamental frequency of vocal fold vibration. The source-filter model separates the repeating excitation from the filter's spectral envelope, explaining how a speaker can change vowel quality without making the same change in pitch.

Praat is software for analyzing, synthesizing, annotating and manipulating speech, created by Paul Boersma and David Weenink. It makes the connection between a recorded acoustic signal and measurable speech properties explicit: a waveform, a spectrogram, a pitch contour and estimated formants describe different aspects of the same recording.^[ref]

For a sustained vowel, one can compare the repeating structure of the waveform with the estimated fundamental frequency, then examine how the frequency spectrum is shaped by the vocal tract. A change in vowel quality need not be a change in pitch. Annotations can align intervals with phonemes or syllables without treating every acoustic boundary as an unambiguous linguistic boundary.

Measurements depend on the analysis settings and the signal. In particular, a displayed pitch contour can contain octave errors, while estimated formants depend on the analysis model. Inspecting the recorded sound and analysis assumptions is therefore part of the experiment, rather than accepting every displayed trajectory as ground truth.

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.

Manner of articulation describes how a speech constriction controls airflow. A plosive builds an oral closure that can be released; a fricative narrows the passage enough to generate turbulent airflow. A nasal consonant can close the oral passage while allowing air to pass through the nose.^[ref]

Compare [p], [f] and [m]. Their differences cannot be reduced to whether the sound comes from the front of the mouth: the closure, friction-producing narrowing and nasal route produce different acoustic consequences. A sustained [f] contains a noise component generated by airflow through a narrow constriction; a sustained [m] combines voicing with a different resonant airway.

Manner of articulation complements place of articulation. Two sounds can share a place but differ in manner, so identifying only the location of a constriction leaves the mechanism underspecified.

An affricate is a consonant with a complete closure followed by a fricated release, treated as one coordinated sound in the analysis of a language. It combines a stop-like beginning with turbulence during release. This manner of articulation differs from a freely combined consonant cluster containing a plosive and a fricative.^[ref]

English jet begins with the affricate [d͡ʒ]; chair begins with [t͡ʃ]. The tie in these transcriptions signals the intended grouping. A recording can reveal the closure and following frication, but those phases alone do not settle whether a language organizes the sound as one unit or two. Contrasts, distribution and articulatory coordination provide further evidence. Counting written letters is especially unreliable: the two letters ch can represent one affricate.

A plosive is an oral stop consonant: articulators form a complete oral closure, pressure can build behind it, and releasing the closure can produce a brief burst. During the closure, the nasal airflow route is normally closed. This distinguishes the mechanism from a nasal consonant with the same oral place of articulation.^[ref]

The sounds [p] and [b] both use a bilabial closure, while differing in their usual voicing classification. A recording of a released [p] can show a closure interval followed by a burst and the following sound. The release need not always be audibly strong, so an absent obvious burst alone does not show that no closure occurred. Articulation and the observed acoustic trace provide complementary evidence.

A fricative is a consonant produced with a narrow constriction that generates sustained turbulent airflow and its associated noise. The articulators approach closely without creating the complete oral closure of a plosive. Place of articulation and voicing further distinguish different fricatives.^[ref]

Sustain [f] and then [v]. Both use the lower lip and upper teeth, but the second normally adds vocal fold vibration. A spectrogram can display a noise component and, where present, periodic structure. The physical source of the noise is the constricted airflow, while the vocal tract shapes its spectrum. Merely calling a sound unvoiced does not identify it as a fricative.

Place of articulation identifies where speech articulators form a constriction or closure. A description can specify an active articulator, such as the tongue, and the surface it approaches. A bilabial consonant uses both lips; a labiodental consonant uses the lower lip and upper teeth; a velar consonant involves the back of the tongue near the soft palate.^[ref]

For example, [f] and [v] share a labiodental location, while their typical voicing classifications differ. Conversely, describing a sound as a fricative specifies manner of articulation without identifying which constriction produces it. The paired descriptions make the physical classification more informative.

The place is an approximate region and relation between articulators, rather than a single universal coordinate in the mouth. Neighboring sounds can change the detailed movement while leaving the broad category useful.

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 labiodental consonant forms its principal constriction between the lower lip and upper teeth. This is a place of articulation, distinct from the two-lip constriction of a bilabial consonant. It does not by itself specify voicing or manner of articulation.^[ref]

The familiar sounds [f] and [v] are labiodental fricatives. Comparing them keeps the constriction location similar while changing the usual voicing category. Comparing [f] with [p] instead changes both the contact surface and the airflow mechanism. A mirror can show lower-lip contact with the upper teeth, while acoustic phonetics examines the resulting noise and periodicity.

A velar consonant forms its main constriction between the back of the tongue and the soft palate. The label identifies a place of articulation. The soft palate's separate role in controlling the nasal airflow route means that velar place does not itself imply a nasal manner of articulation.^[ref]

The sounds [k] and [g] are velar oral stops, while [ŋ] is a velar nasal consonant. All involve a similar oral constriction region, but they differ in airflow route and usual voicing. The precise contact position can also shift with neighboring vowels. Describing a region of contact is therefore more informative than imagining one fixed point used identically in every utterance.

Voicing is the use of vocal fold vibration during speech production. Airflow and the mechanical state of the vocal folds can sustain repeated opening and closing, introducing a periodic component into the emitted sound. The fundamental frequency of this repetition contributes to perceived pitch.

A practical comparison is to sustain [s] and [z] while gently feeling the front of the throat: the added vibration during [z] makes the distinction tangible. Both involve a similar oral constriction, so the comparison separates voicing from place of articulation and manner of articulation. The physical state of the glottis is an additional dimension of the sound.^[ref]

A binary transcription is a useful classification rather than a complete time record. Voicing can begin, end or weaken during a sound, and an acoustic estimate depends on the interval examined. A pitch contour should therefore distinguish missing or unreliable periodicity from a measured low fundamental frequency.

A grouping of speech sounds defined by a relevant perceptual or articulatory organisation. Experimental discrimination of two endpoints does not, by itself, establish a complete inventory of linguistic categories.