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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.

Canadian English names English varieties used in Canada, with variation across regions, communities and speakers. For a scientific account, a pronunciation feature must be operationalized and measured rather than treated as a property shared identically by every speaker. Sociolinguistics and acoustic phonetics provide complementary methods for those comparisons.

An acoustic study by Sky Onosson compared Canadian, American Western and American Northern speech through vowel durations and formant trajectories, examining Canadian raising and the effect of a following consonant's voicing.^[ref] A useful replication would record comparable words and contexts, align vowel intervals, and compare trajectories under a stated time normalization. That separates a pronunciation's changing acoustic shape from differences caused merely by speaking rate or the analysis point.

Canadian raising names a pronunciation pattern in which the starting portion of the diphthongs conventionally transcribed /aɪ/ and /aʊ/ is raised in particular contexts, especially before a voiceless syllable coda. The pattern is associated with Canadian English, while related effects also occur in other North American varieties.^[ref]

Comparing lout and loud in controlled contexts can illustrate a voiceless-versus-voiced following consonant, but an acoustic test should compare repeated tokens and their formant trajectories. Sky Onosson's dissertation separates changes in trajectory from the shortening of vowels before voiceless consonants; its abstract reports different cross-dialect patterns for the two diphthongs. A single midpoint or duration can therefore miss part of the phenomenon. Raising refers to vowel quality, not simply to a higher voice fundamental frequency.

David Weenink co-created Praat with Paul Boersma, providing tools for measuring and modeling speech. His 2006 thesis investigated speaker-adaptive vowel identification: how recognition can remain useful when acoustic patterns vary between speakers.^[ref][ref]

The thesis describes recordings from 30 speakers, each producing 12 Dutch vowels in controlled sentence frames. It relates these data to formants, principal component analysis, discriminant analysis and adaptive classification methods. This makes the recognition problem experimentally concrete: a classifier must separate vowel identity from speaker-related variation rather than memorize a single speaker's frequency spectrum.^[ref]

Homepage: www.fon.hum.uva.nl/david/

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.

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.

Gunnar Fant developed acoustic models connecting the physical production of speech to its measurable signal. His Acoustic Theory of Speech Production by Gunnar Fant relates vocal-tract geometry to acoustic behavior, including calculations based on X-ray studies of articulations. The original book dates to 1960; the inspected publisher preview is its 1970 second printing.^[ref]

His source-filter model of speech production separates excitation from the filtering of the vocal tract. Changing a filter's resonances can move formants without requiring the same change in the fundamental frequency of the source. This makes speech synthesis an experimental tool: a researcher can vary model parameters and compare the generated signal with recorded speech. KTH's account explicitly describes his synthesis work as a means of testing production hypotheses.^[ref]

KTH's curriculum vitae records 1919–2009 and his leadership of the Speech Transmission Laboratory from 1951 to 1966.^[ref]

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.

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 phonetician studies the physical production, transmission or perception of speech. Articulatory phonetics investigates the moving vocal tract, acoustic phonetics measures recorded sound, and auditory phonetics studies listeners' responses. One research question can require evidence from more than one of these stages.

For example, a phonetician investigating a vowel contrast can record repeated tokens, estimate formants and test whether listeners distinguish the recordings. Speaker variation and analysis settings must be controlled or measured before differences are attributed to the contrast. Praat provides tools for waveform, spectrogram, pitch contour and formant analysis, making several of these observations reproducible.^[ref] The profession therefore connects language questions to instruments, explicit annotation rules and testable measurements.

A pitch contour describes how perceived pitch varies over an utterance. For speech with voicing, a common measurable correlate is the fundamental frequency $F_0(t)$ of vocal fold vibration. A rising estimated $F_0(t)$ indicates increasing repetition rate; stretches without sufficiently periodic vibration need not have a meaningful estimate.^[ref]

For an ideal periodic segment whose repetitions are separated by $T=0.01\mathrm{s}$, $F_0=1/T=100\mathrm{Hz}$. Detecting repetition at $2T$ instead produces an erroneous 50 hertz estimate, illustrating why a visually smooth pitch contour can still contain an octave error. Noise, the analysis interval and the allowed frequency range affect the estimate. Current Praat documentation distinguishes methods intended for speech intonation from methods intended for other periodicity measurements.^[ref]

A pitch contour is not the same as a formant contour: changing the fundamental frequency changes the repetition rate, whereas formants describe the resonant spectral structure shaped by the vocal tract.

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.

Sky Onosson is a linguist whose research connects phonetics, phonology and quantitative analysis of language variation. His research statement emphasizes the changing acoustic structure of vowels, including diphthongs, and the use of the R for modeling and visualization.^[ref]

His 2018 dissertation investigated Canadian raising by comparing vowel duration and formant trajectories across Canadian and two American dialect groups.^[ref] Comparing a trajectory instead of only one instant helps distinguish a vowel's changing quality from the effects of duration. His work consequently treats time alignment as part of the scientific analysis, rather than assuming that measurements at a single relative time capture every contrast.

Homepage: onosson.github.io/

The source-filter model of speech production represents a speech sound as an acoustic source shaped by a filter describing the vocal tract. During voiced speech, vibration of the vocal folds supplies a roughly periodic source; constrictions can also generate noise. The tract's resonances emphasize particular frequency regions called formants.^[ref]

Paul Boersma credits Gunnar Fant's 1960 account as the theoretical basis of this construction.^[ref]

In a simplified linear model, output spectrum $Y(f)$ is $S(f)H(f)$, where $S$ describes the source and $H$ the tract's transfer function. Keeping the source fixed while changing the filter can change vowel quality without changing the source's fundamental repetition rate. The Praat tutorial makes this test concrete by constructing a source signal and a formant filter separately, then combining them. The model's separation is an approximation; real sources and tracts can interact.^[ref]

Speech synthesis generates an artificial speech signal from a specified representation. Text-to-speech starts from writing, while a research synthesizer can instead take a phonetic specification or directly controlled acoustic parameters. The distinction separates the input representation from the mechanism producing the sound.

In a source-filter model of speech production, a researcher can set an excitation's fundamental frequency and independently adjust the filter's formants. Holding the first parameter fixed while moving a formant tests whether listeners' responses depend on the spectral change rather than a change in voice pitch. Gunnar Fant's work at KTH used synthesis to test hypotheses about speech production.^[ref] Generated stimuli permit controlled comparisons in speech perception, but intelligibility and similarity to a natural speaker are different outcomes. Recording the parameter settings makes a synthesis experiment reproducible.

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.

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.

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.