= Pitch contour
{title2=$F_0(t)$}
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.<Pitch Analysis in the Praat Manual by Paul Boersma>[Intro4: the pitch contour and its configuration]{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.<Pitch Analysis in the Praat Manual by Paul Boersma>[How to choose a pitch analysis method: autocorrelation, filtering and octave errors; https://uvafon.hum.uva.nl/praat/manual/how_to_choose_a_pitch_analysis_method.html]{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>.
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