Editing Vowel (section)

== Acoustics ==
{{hatnote|Related article: [[Phonetics]]}}
[[File:Spectrogram -iua-.png|thumb|upright=1.8|Spectrogram of vowels {{IPA|[i, u, ɑ]|cat=no}}. {{IPA|[ɑ]}} is a low vowel, so its F1 value is higher than that of {{IPA|[i]}} and {{IPA|[u]}}, which are high vowels. {{IPA|[i]}} is a front vowel, so its F2 is substantially higher than that of {{IPA|[u]}} and {{IPA|[ɑ]}}, which are back vowels.]]
{{multiple image
| align = right
| direction = vertical
| image1 = Vowel triange, cardinal vowels.png
| caption1 = An idealized schematic of vowel space, based on the formants of [[Daniel Jones (phonetician)|Daniel Jones]] and [[John C. Wells|John Wells]] pronouncing the cardinal vowels of the IPA. The scale is logarithmic. The grey range is where F2 would be less than F1, which by definition is impossible. {{IPA|[a]}} is an extra-low central vowel. Phonemically it may be front or back, depending on the language. Rounded vowels that are front in tongue position are front-central in formant space, while unrounded vowels that are back in articulation are back-central in formant space. Thus {{IPA|[y ɯ]}} have perhaps similar F1 and F2 values to the high central vowels {{IPA|[ɨ ʉ]}}, being distinguished by rounding (F3); similarly {{IPA|[ø ɤ]}} vs central {{IPA|[ɘ ɵ]}} and {{IPA|[œ ʌ]}} vs central {{IPA|[ɜ ɞ]}}.
| image2 = Vowel triangle, intermediate vowels.png
| caption2 = The same chart, with a few intermediate vowels. Low front {{IPA|[æ]}} is intermediate between {{IPA|[a]}} and {{IPA|[ɛ]}}, while {{IPA|[ɒ]}} is intermediate between {{IPA|[ɑ]}} and {{IPA|[ɔ]}}. The back vowels change gradually in rounding, from unrounded {{IPA|[ɑ]}} and slightly rounded {{IPA|[ɒ]}} to tightly rounded {{IPA|[u]}}; similarly slightly rounded {{IPA|[œ]}} to tightly rounded {{IPA|[y]}}. With {{IPA|[a]}} seen as an (extra-)low central vowel, the vowels {{IPA|[æ ɐ ɑ]}} can be redefined as front, central and back (near-)low vowels.
}}

The acoustics of vowels are fairly well understood. The different vowel qualities are realized in acoustic analyses of vowels by the relative values of the [[formant]]s, acoustic [[resonance]]s of the vocal tract which show up as dark bands on a [[spectrogram]]. The vocal tract acts as a [[resonant cavity]], and the position of the jaw, lips, and tongue affect the parameters of the resonant cavity, resulting in different formant values. The acoustics of vowels can be visualized using spectrograms, which display the acoustic energy at each frequency, and how this changes with time.

The first formant, abbreviated "F1", corresponds to vowel openness (vowel height). [[Open vowel]]s have high F1 frequencies, while [[close vowel]]s have low F1 frequencies, as can be seen in the accompanying spectrogram: The {{IPA|[i]}} and {{IPA|[u]}} have similar low first formants, whereas {{IPA|[ɑ]}} has a higher formant.

The second formant, F2, corresponds to vowel frontness. [[Back vowel]]s have low F2 frequencies, while [[front vowel]]s have high F2 frequencies. This is very clear in the spectrogram, where the front vowel {{IPA|[i]}} has a much higher F2 frequency than the other two vowels. However, in open vowels, the high F1 frequency forces a rise in the F2 frequency as well, so an alternative measure of frontness is the ''difference'' between the first and second formants. For this reason, some people prefer to plot as F1 vs. F2&nbsp;–&nbsp;F1. (This dimension is usually called 'backness' rather than 'frontness', but the term 'backness' can be counterintuitive when discussing formants.)

In the third edition of his textbook, [[Peter Ladefoged]] recommended using plots of F1 against F2&nbsp;–&nbsp;F1 to represent vowel quality.<ref>Ladefoged, Peter (1993) ''A Course in Phonetics (Third Edition)'', Fort Worth: Harcourt Brace Jovanovich, p. 197.</ref> However, in the fourth edition, he changed to adopt a simple plot of F1 against F2,<ref>Ladefoged, Peter (2001) ''A Course in Phonetics (Fourth Edition)'', Fort Worth: Harcourt, p. 177.</ref> and this simple plot of F1 against F2 was maintained for the fifth (and final) edition of the book.<ref>Ladefoged, Peter (2006) ''A Course in Phonetics (Fifth Edition)'', Boston: Thomson Wadsworth, p. 189.</ref> Katrina Hayward compares the two types of plots and concludes that plotting of F1 against F2&nbsp;–&nbsp;F1 "is not very satisfactory because of its effect on the placing of the central vowels",<ref>Hayward, Katrina (2000) ''Experimental Phonetics'', Harlow, UK: Pearson, p. 160.</ref> so she also recommends use of a simple plot of F1 against F2. In fact, this kind of plot of F1 against F2 has been used by analysts to show the quality of the vowels in a wide range of languages, including RP,<ref>{{Cite journal | doi = 10.1017/S0025100300005417 | author = Deterding, David | year = 1997 | title = The formants of monophthong vowels in Standard Southern British English Pronunciation | journal = Journal of the International Phonetic Association | volume = 27 | issue = 1–2| pages = 47–55 | s2cid = 146157247 }}</ref><ref>{{Cite journal | doi = 10.1017/S0025100305002124 | author = Hawkins, Sarah and Jonathan Midgley | year = 2005 | title = Formant frequencies of RP monophthongs in four age groups of speakers | journal = Journal of the International Phonetic Association | volume = 35 | issue = 2| pages = 183–199 | s2cid = 53532910 }}</ref> the Queen's English,<ref>Harrington, Jonathan, Sallyanne Palethorpe and Catherine Watson (2005) Deepening or lessening the divide between diphthongs: an analysis of the Queen's annual Christmas broadcasts. In William J. Hardcastle and Janet Mackenzie Beck (eds.) '' A Figure of Speech: A Festschrift for John Laver'', Mahwah, NJ: Lawrence Erlbaum, pp. 227-261.</ref> American English,<ref>{{Cite journal | doi = 10.1017/S0025100306002817 | author = Flemming, Edward and Stephanie Johnson | year = 2007 | title = Rosa's roses: reduced vowels in American English | url = http://web.mit.edu/flemming/www/paper/reduced-rev2.pdf| journal = Journal of the International Phonetic Association | volume = 37 | pages = 83–96 | citeseerx = 10.1.1.536.1989 | s2cid = 145535175 }}</ref> Singapore English,<ref>{{Cite journal | doi = 10.1075/eww.24.1.02det | author = Deterding, David | year = 2003 | title = An instrumental study of the monophthong vowels of Singapore English | journal = English World-Wide | volume = 24 | pages = 1–16 }}</ref> Brunei English,<ref>{{Cite journal | doi = 10.1075/eww.27.3.03sha | author = Salbrina, Sharbawi | year = 2006 | title = The vowels of Brunei English: an acoustic investigation | journal = English World-Wide | volume = 27 | issue = 3| pages = 247–264 }}</ref> North Frisian,<ref>{{Cite journal | doi = 10.1017/S002510030400180X |author1-link=Ocke-Schwen Bohn | author = Bohn, Ocke-Schwen | year = 2004 | title = How to organize a fairly large vowel inventory: the vowels of Fering (North Frisian) | url = http://pure.au.dk/portal/files/44857633/jipa34.pdf | journal = Journal of the International Phonetic Association | volume = 34 | issue = 2| pages = 161–173 | s2cid = 59404078 }}</ref> Turkish Kabardian,<ref>{{Cite journal | doi = 10.1017/S0025100306002532 | author = Gordon, Matthew and Ayla Applebaum | year = 2006 | title = Phonetic structures of Turkish Kabardian | url = http://www.linguistics.ucsb.edu/faculty/gordon/kabardianphonetics.pdf| journal = Journal of the International Phonetic Association | volume = 36 | issue = 2| pages = 159–186 | citeseerx = 10.1.1.233.1206 | s2cid = 6665600 }}</ref> and various indigenous Australian languages.<ref>Fletcher, Janet (2006) Exploring the phonetics of spoken narratives in Australian indigenous languages. In William J. Hardcastle and Janet Mackenzie Beck (eds.) '' A Figure of Speech: A Festschrift for John Laver'', Mahwah, NJ: Lawrence Erlbaum, pp. 201–226.</ref>

[[R-colored vowel]]s are characterized by lowered F3 values.

Rounding is generally realized by a decrease of F2 that tends to reinforce vowel backness. One effect of this is that back vowels are most commonly rounded while front vowels are most commonly unrounded; another is that rounded vowels tend to plot to the right of unrounded vowels in vowel charts. That is, there is a reason for plotting vowel pairs the way they are.