Formant

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Spectrogram of American English vowels [i, u, ɑ] showing the formants f₁ and f₂

A formant is a peak in an acoustic frequency spectrum which results from the resonant frequencies of any acoustical system. It is most commonly invoked in phonetics or acoustics involving the resonant frequencies of vocal tracts or musical instruments. However, it is equally valid to talk about the formant frequencies of the air in a room, as exploited, for example, by Alvin Lucier in his piece I am sitting in a room.

Formants are the distinguishing or meaningful frequency components of human speech and of singing. By definition, the information that humans require to distinguish between vowels can be represented purely quantitatively by the frequency content of the vowel sounds. Formants are the characteristic partials that identify vowels to the listener. 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 formant with the lowest frequency is called f₁, the second f₂, and the third f₃. Most often the two first formants, f₁ and f₂, are enough to disambiguate the vowel. These two formants are primarily determined by the position of the tongue. f₁ has a higher frequency when the tongue is lowered, and f₂ has a higher frequency when the tongue is forward. Generally, formants move about in a range of approximately 1000 Hz for a male adult, with 1000 Hz per formant. Vowels will almost always have four or more distinguishable formants; sometimes there are more than six.

Nasals usually have an additional formant around 2500 Hz. The liquid [l] usually has an extra formant at 1500 Hz, while the English "r" sound (IPA [ɹ]) is distinguished by virtue of a very low third formant (well below 2000 Hz).

Plosives (and, to some degree, fricatives) modify the placement of formants in the surrounding vowels. Bilabial sounds (such as 'b' and 'p' as in "ball" or "sap") cause a lowering of the formants; velar sounds ('k' and 'g' in English) almost always show f₂ and f₃ coming together in a 'velar pinch' before the velar and separating from the same 'pinch' as the velar is released; alveolar sounds (English 't' and 'd') cause less systematic changes in neighboring vowel formants, depending partially on exactly which vowel is present. The time-course of these changes in vowel formant frequencies are referred to as 'formant transitions'.

If the fundamental frequency of the underlying vibration is higher than the formant frequency of the system, then the character of the sound imparted by the formant frequencies will be mostly lost. This is most apparent in the example of soprano opera singers, who sing high enough that their vowels become very hard to distinguish.

Control of formants is an essential component of the vocal technique known as overtone singing, in which the performer sings a low fundamental tone, and creates sharp resonances to select upper harmonics, giving the impression of several tones being sung at once.

Spectrograms are used to visualise formants.

**Vowel formant centers**
Vowel	IPA	Formant f₁	Formant f₂
u	u	320 Hz	800 Hz
o	o	500 Hz	1000 Hz
ɑ	aː	700 Hz	1150 Hz
a	a	1000 Hz	1400 Hz
ø	ø	500 Hz	1500 Hz
y	y	320 Hz	1650 Hz
æ	ɛ	700 Hz	1800 Hz
e	e	500 Hz	2300 Hz
i	i	320 Hz	3200 Hz

**Vowel formants**
Vowel	Main formant region
u	200 to 400 Hz
o	400 to 600 Hz
a	800 to 1200 Hz
e	400 to 600 and 2200 to 2600 Hz
i	200 to 400 and 3000 to 3500 Hz

[edit] Singers' formant

Studies of the frequency spectrum of trained singers, especially male singers, indicate a clear formant around 3000 Hz (between 2800 and 3400) that is absent in speech or in the spectra of untrained singers. It is this formant which allows singers to be heard and understood over an orchestra. This formant is actively developed through vocal training, for instance through so-called voce di strega exercises.