Question

Summarize the Acoustic Theory of Speech/Vowel Production

Answer 1

Acoustic theory explains production and perception of speech by utilizing concept of distinctive features. However, for some phonemes and even for some syllables or words, recognition might be possible immediately without prior analysis into distinctive features. The acoustic theory is dependent upon the extraction from the acoustic signal of those physical characteristics, which represent the distinctive features.

The thesis of this theory is that speech sounds can be understood in terms of a source of energy that is filtered by the vocal tract. The quasiperiodic vibration of the vocal folds produces the energy source known as voicing.

This source has a harmonic spectrum in which the energy of the harmonic components falls off at the rate of 12 dB/octave. This energy activates the resonances (formants of the vocal tract). The resonances act like a filter, such that the energy in the various harmonics of the source is not transmitted equally.

Although there are theoretically an infinite number of formants, we are concerned primarily with the first three formants. One reason is that energy of the source is greatest in the low frequencies that include these three formants. Further, three formants are sufficient to account for most phonetic variations for vowels in the world's languages.