What is the effect of a smaller vocal tract on formant frequencies?

A smaller vocal tract tends to produce higher formant frequencies. This phenomenon is rooted in the physical properties of sound waves and the resonant characteristics of the vocal tract. When the length of the vocal tract decreases, it effectively changes the way sound resonates within it.

Specifically, the fundamental frequency and the formants (which are the resonant frequencies of the vocal tract) are affected by the size and shape of this tract. A shorter vocal tract results in a closer spacing of formant frequencies and a general increase in their overall frequencies. As a result, the first few formants are raised in frequency, which contributes to the perception of higher pitched sounds or vowels.

In contrast, if the vocal tract is longer, the formants are lower in frequency, which can give the impression of a deeper voice. The relationship between the size of the vocal tract and the resulting formant frequencies is a key aspect of speech science, leading to variations in how different phonemes are produced and perceived.