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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.

Speech intonation is the pattern of pitch variation across an utterance. Its acoustic description commonly uses a pitch contour, tracking the estimated fundamental frequency through voiced portions of speech. The pitch contour describes one component of prosody; it does not by itself encode every distinction conveyed by emphasis, pauses or timing.

To investigate it, record the same phrase with different intended emphasis, then align the recordings by their words and compare the pitch contours. Inspect the underlying waveform as well as the automatic estimate: a tracking error can resemble an abrupt jump. The analysis range matters, and a low pitch floor requires a longer time window, trading the ability to detect low fundamental frequencies against the resolution of rapid changes.^[ref]

An estimated fundamental frequency should not be read as a measured vocal oscillation during a genuinely unvoiced interval. Nor does a rise have a universal meaning independently of the language and conversational setting.

A syllable organizes speech sounds around a syllable nucleus, often a vowel. A preceding syllable onset and a following syllable coda can surround that nucleus. These components describe the organization of speech, rather than a requirement to pause between successive units.^[ref]

For example, in a simple pronunciation of “cat”, [k] occupies the onset, [æ] the nucleus and [t] the coda. A syllable can have an empty onset or coda, so the example's three-part form is not a mandatory template for every word. A syllabic consonant can also serve as a nucleus.

The distinction matters in speech rhythm: counting letters, counting phonemes and identifying syllables are different operations. Physical measurements of duration and pitch contours can be related to syllable organization, but they do not imply a silent gap at every proposed boundary.

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.