Source Filter Theory by Gunnar Fant 1960


In acoustic phonetics¡Bsource refers to the wave form of the vibrating larynx. Its spectrum is rich in harmonics¡Bwhich gradually decrease in amplitude as their frequency increases. The various resonance chambers of the vocal tract¡Bespecially the movements of the tongue and lips¡Bthen act on the laryngeal source in the manner of a filter¡Breinforcing certain harmoncis relative to others. The combination of these two elements is known as the source-filter model of vowel production.

The complex waves produced during voiced periods of speech depend on two things:

  1. the waves produced by the vocal cord vibrations (the source)¡Band
  2. the way those waves are modified by the higher parts of the vocal tract (the filter).

An important feature of the source are its harmonics. One of the most important ideas in understanding the filter is resonance.