Formant

In speech science and phonetics, a formant is the broad spectral maximum that results from an acoustic resonance of the human vocal tract.

From an acoustic point of view, phonetics had a serious problem with the idea that the effective length of vocal tract changed vowels.

Therefore, it was unclear how vowels could depend on frequencies when talkers with different vocal tract lengths, for instance bass and soprano singers, can produce sounds that are perceived as belonging to the same phonetic category.

[6] Formants are distinctive frequency components of the acoustic signal produced by speech, musical instruments[8] or singing.

The information that humans require to distinguish between speech sounds can be represented purely quantitatively by specifying peaks in the frequency spectrum.

Most of these formants are produced by tube and chamber resonance, but a few whistle tones derive from periodic collapse of Venturi effect low-pressure zones.

The relationship between the perceived vowel quality and the first two formant frequencies can be appreciated by listening to "artificial vowels" that are generated by passing a click train (to simulate the glottal pulse train) through a pair of bandpass filters (to simulate vocal tract resonances).

In normal voiced speech, the underlying vibration produced by the vocal folds resembles a sawtooth wave, rich in harmonic overtones.

This is most apparent in the case of soprano opera singers, who sing at pitches high enough that their vowels become very hard to distinguish.

Formants, whether they are seen as acoustic resonances of the vocal tract, or as local maxima in the speech spectrum, like band-pass filters, are defined by their frequency and by their spectral width (bandwidth).

The first two formants are important in determining the quality of vowels, and are frequently said to correspond to the open/close (or low/high) and front/back dimensions (which have traditionally been associated with the shape and position of the tongue).