We saw in the last chapters that speech sounds can be discussed in terms of their articulation – the physical processes involved in speech production. The focus of this chapter is another area of phonetics which deals with the physical properties of speech sounds. When sounds are produced in the mouth they have speciﬁc, measurable effects on the air involved. Acoustic phonetics is the study of these effects. Just as speech sounds can be distinguished by their manner of articulation, say stops vs. fricatives, they can also be distinguished by speciﬁc physical properties, for example the acoustic correlates typically associated with obstruents vs. sonorants.