= Acoustic phonetics
<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.<Spectral Analysis in the Praat Manual by Paul Boersma>[Intro 3.1, time–frequency axes, energy display, formant measurements and the analysis window]{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>.
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