Vowels, nasal, lateral and median approximants, taps and trill are all sonorant sounds. The opposite of sonorant is obstruent . A ranking of sound types depending on their their sonority , which is usually defined as the degree of resistance of an articulation to free airflow through the vocal tract, where higher resistance equals lower sonority. There are a number of versions of the hierarchy to be found in the the literature. The hierarchy is used define universal tendencies in syllable structure.
Syllables tend to increase in sonority towards the centre and then decrease towards the end.
A graph of the variation of spectral shape as a function of time. Spectrograph A machine used to produce a spectrogram. It is usual nowadays to use a computer program for this task. Speech sound Any sound produced by the human vocal tract which is found as part of the make-up of words in some human language, or a copy of such a sound produced synthetically. Speech pressure waveform A graph of the variation of pressure as a function of time during the production of speech.