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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.

Prosody comprises patterns of pitch, timing and emphasis extending across the individual segments of speech. Speech intonation concerns the changing pitch pattern, while speech rhythm concerns the temporal organization. The same sequence of words can be spoken with different prosody.

For acoustic analysis, a recording is examined over time. A spectrogram can reveal changes in the fundamental frequency of voiced portions; segment durations and pauses provide timing measurements. The perceived pitch and emphasis are perceptual judgments, so they should be distinguished from the measured frequency and sound pressure. Phonetics relates the recorded signal to its production and perception.

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.

Speech rhythm is the temporal organization of speech: the durations and grouping of segments, syllables, pauses and prominent portions of an utterance. It is one component of prosody, distinct from the changing pitch pattern of speech intonation.

An original measurement exercise is to record several repetitions of a short phrase at a comfortable rate, then again more quickly. Mark the same chosen boundaries on each recording and compare the elapsed times between them. Normalizing an interval by the utterance's total duration distinguishes uniform speeding-up from redistribution of time within the phrase. The result depends on which boundaries were marked, so the annotation rule is part of the measurement method. Software such as Praat stores labelled time intervals in separate annotation tiers, allowing the audio and its proposed segmentation to be inspected together.^[ref]

Perceived rhythmic prominence is not simply the height of the sound pressure waveform. Duration, pitch and intensity can contribute differently, and a claim about regular timing requires measured intervals rather than an impression of a beat.