Voice or voicing is a term used in phonetics and phonology to characterize speech sounds, with sounds described as either voiceless (unvoiced) or voiced. The term, however, is used to refer to two separate concepts. Voicing can refer to the articulatory process in which the vocal cords vibrate. This is its primary use in phonetics to describe phones, which are particular speech sounds. It can also refer to a classification of speech sounds that tend to be associated with vocal cord vibration but need not actually be voiced at the articulatory level. This is the term's primary use in phonology when describing phonemes, or in phonetics when describing phones.
At the articulatory level, a voiced sound is one in which the vocal cords vibrate, and a voiceless sound is one in which they do not. Voicing is the difference between the pairs of sounds that are associated with the English letters "s" and "z". The two sounds are symbolically written [s] and [z] to distinguish them from the English letters, which have several possible pronunciations depending on context. If one places the fingers on the voice box (ie the location of the Adam's apple in the upper throat), one can feel a vibration when one pronounces zzzz, but not when one pronounces ssss. (For a more detailed, technical explanation, see modal voice and phonation.) In European languages such as English, vowels and other sonorants (consonants such as m, n, l, and r) are modally voiced.
The distinction between the articulatory use of voice and the phonological use rests on the distinction between phone and phoneme. The difference is best illustrated by a rough example. Words are composed of phonemes. The English word "pods" is made up of a sequence of phonemes, represented symbolically as "/padz/", or the sequence of /p/, /a/, /d/, and /z/. Each letter is an abstract symbol for a phoneme. This is a part of our grammatical knowledge.
Consonant phonemes are classified as either voiced or voiceless. Some voiced phonemes of English are /b,d,g,v,z/. Each of these obstruents has an unvoiced counterpart, /p,t,k,f,s/. The classification is useful for describing phonological processes such as vowel lengthening that occurs before voiced consonants but not before unvoiced consonants or vowel quality changes (i.e. the sound of the vowel) in some dialects of English that occur before unvoiced but not voiced consonants.
However, phonemes are not sounds. Rather, phonemes are, in turn, converted to phones before being spoken. The /z/ phoneme, for instance, can be pronounced as the [s] phone or the [z] phone, depending on context, and so the sequence of phones for "pods" might be [pads] or [padz]. The different type of brackets indicates that these are symbols for phones now. As described above, while the [z] phone has articulatory voicing, the [s] phone does not. It is hard to directly observe the difference between [pods] and [podz] because of the voicing in the preceding [d], but one can readily see that both pronunciations are common using digital audio tools.
English has four pairs of fricative phones which can be divided into a table by place of articulation and voicing. The voiced fricatives can readily be felt to have voicing throughout the duration of the phone.
However, in a class of consonants called plosives, such as [p, t, k, b, d, g], the contrast is more complicated and can vary from language to language. Articulatory voicing does not generally occur throughout the sound since airflow is blocked by the tongue in the pronunciation of the consonant ("closure"). The difference between the unvoiced plosive phones and the voiced plosive phones is not just a matter of whether (articulatory) voicing is present or not. Rather, it includes when voicing starts (if at all), the presence of aspiration (airflow burst following the release of the closure), and the duration of the closure and of the aspiration.
English voiceless plosives are generally aspirated or have longer aspiration than their voiced counterparts, do not have any voicing until after the aspiration (this is really the voicing of the following sound), and have a longer closure duration than their voiced counterparts. The voiced plosives can have voicing during closure, though often do not. The phone symbols are sometimes strictly considered to represent the presence of articulatory voicing, in addition with aspiration represented as a separate symbol (a superscript h), though these symbols may informally represent something more useful for the language at hand.
When these consonants come at the end of a syllable, however, such as at the end of a word, in many English dialects there is often little or no aspiration. The closure is not released, making it sometimes difficult to hear the difference between these pairs of word-final consonants. However, other auditory cues remain, such as what has been described above: the length of the preceding vowel and of the consonant itself.
Finally, there is a class of consonants called affricates which combines the properties of plosive and fricative:
Other English sounds, the vowels, nasals, and liquids (called sonorants), are normally fully voiced. However, these consonants and unstressed vowels may be devoiced in certain positions, especially after aspirated consonants, as in police, tree, and play, where the voicing is delayed to the extent of missing the sonorant altogether.
Beside the pairs of voiceless and voiced 'obstruent' consonants given above, other voiced sounds in English are the nasals, i.e. /m, n, ŋ/; the approximants, i.e. /l, r, w, j/ (the last spelled as the English letter <y>); and the vowels. These sounds are called sonorants.
Degrees of voicing
There are two variables to degrees of voicing: intensity (discussed under phonation), and duration (discussed under voice onset time). When a sound is described as "half voiced" or "partially voiced", it is not always clear whether that means that the voicing is weak (low intensity), or if the voicing only occurs during part of the sound (short duration). In the case of English, it is the latter.
Voice and tenseness
There are languages with two sets of contrasting obstruents that are labelled /p t k f s x …/ vs. /b d ɡ v z ɣ …/ even though there is no involvement of voice (or voice onset time) in that contrast. This happens for instance in several Southern German dialects such as Alsatian or Swiss German. Since voice is not involved, this is explained as a contrast in tenseness, called a fortis and lenis contrast.
There is a hypothesis that the contrast between fortis and lenis consonants is related to the contrast between voiceless and voiced consonants, a relation based on sound perception as well as on sound production, where consonant voice, tenseness and length are but different manifestations of a common sound feature.
Published - November 2008
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