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A formant, as used by James Jeans,〔Jeans, J.H. (1938) Science & Music, reprinted by Dover, 1968.〕 is a harmonic of a note that is augmented by a resonance. The speech researcher Gunnar Fant〔Fant, G. (1960). Acoustic Theory of Speech Production. Mouton & Co, The Hague, Netherlands.〕 defines formants as "the spectral peaks of the sound spectrum |P(f)|". In acoustics generally, a very similar definition is widely used: the Acoustical Society of America defines a formant as: "a range of frequencies (a complex sound ) in which there is an absolute or relative maximum in the sound spectrum".〔Standards Secretariat, Acoustical Society of America, (1994). ANSI S1.1-1994 (R2004) American National Standard Acoustical Terminology, (12.41) Acoustical Society of America, Melville, NY.〕 In speech science and phonetics, however, a formant is also sometimes used to mean an acoustic resonance〔Titze, I.R. (1994). Principles of Voice Production, Prentice Hall, ISBN 978-0-13-717893-3.〕 of the human vocal tract. Thus, in phonetics, formant can mean either a resonance or the spectral maximum that the resonance produces. Formants are often measured as amplitude peaks in the frequency spectrum of the sound, using a spectrogram (in the figure) or a spectrum analyzer and, in the case of the voice, this gives an estimate of the vocal tract resonances. In vowels spoken with a high fundamental frequency, as in a female or child voice, however, the frequency of the resonance may lie between the widely spaced harmonics and hence no corresponding peak is visible. A room can be said to have formants characteristic of that particular room, due to the way sound reflects from its walls and objects. Room formants of this nature reinforce themselves by emphasizing specific frequencies and absorbing others, as exploited, for example, by Alvin Lucier in his piece ''I Am Sitting in a Room''. ==Formants and phonetics== Formants are distinctive frequency components of the acoustic signal produced by speech or singing. The information that humans require to distinguish between speech sounds can be represented purely quantitatively by specifying peaks in the amplitude/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 formant with the lowest frequency is called ''F''1, the second ''F''2, and the third ''F''3. Most often the two first formants, ''F''1 and ''F''2, are enough to disambiguate the vowel. 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). An interactive demonstration of this can be found (here ). Nasal consonants usually have an additional formant around 2500 Hz. The liquid usually has an extra formant at 1500 Hz, whereas the English "r" sound () is distinguished by 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 and in "ball" or "sap") cause a lowering of the formants; velar sounds ( and in English) almost always show ''F''2 and ''F''3 coming together in a 'velar pinch' before the velar and separating from the same 'pinch' as the velar is released; alveolar sounds (English and ) cause less systematic changes in neighbouring 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 a resonance frequency of the system, then the formant usually imparted by that resonance 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 resonances 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「formant」の詳細全文を読む スポンサード リンク
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