ABSTRACT
The vocal tract is a fleshy tube, the shape of which can be altered by the actions of the speech organs. A sound is created by the vibrating vocal folds and it is then modified by passing through the tube. This, in essence, is the source-filter model (or theory) of speech production. Source is a good name for the role of the sound made by the vocal folds, but the term filter may seem obscure. It refers to the role of the vocal tract in modifying the sound created by the vocal folds. The difference between the sound created by the vocal folds and the corresponding sound that emerges into the open air is explained by the “filtering” action of the vocal tract, which determines the amount of energy allowed to pass through, at different frequencies. The most notable modification made by the vocal tract is the introduction of formants (see chap. 11), that is, peaks in the spectrum. This chapter is concerned with the relationship between vocal tract shape and formant frequencies.
