Phonation is the process by which the larynx, or voice box, produces sounds. Depending upon the sub-field of phonetics, phonation may refer only to the quasi-periodic vibration of the vocal cords that produces voiced sounds, or it may refer to any manipulation of the vocal stream by the larynx. In addition to voicing, phonetic features affected by the larynx include creaky voice and breathy voice. The larynx is also responsible for glottal sounds, such as the glottal stop, pronounced between the vowels in the English "uh-oh."
Phoneticians who study laryngeal anatomy and speech production often take phonation to mean only the quasi-periodic vibration of the vocal cords. You can tell if a sound has this type of phonation by placing your fingers on the front of your throat, and feeling for vibration during speech. If the vocal cords are vibrating during speech, a voiced sound is produced. Voiced sounds include all vowels and nasal sounds in English, as well as consonants like /b/, /v/, /d/, /z/, and /g/. The voiceless counterparts of these consonants, /p/, /f/, /t/, /s/, and /k/ respectively, differ from the voiced versions only in the lack of vibration of the vocal cords.
Some languages have more voice distinctions than simply voiced and voiceless, and many linguists use phonation to refer to any manipulation of sounds by the glottis. In addition to voiced and voiceless sounds, some languages have creaky-voiced or laryngealized sounds, produced with very tense vocal cords, and breathy-voiced or murmured sounds, produced with minimal tension in the vocal cords. Voiceless sounds are produced with no tension at all in the vocal cords. Beyond these distinctions, some languages use slack voice, with more tension than a murmured sound, but less than a voiced sound, and some include stiff voice, with tension of the vocal cords somewhere between that required for a voiced sound and that required for a laryngealized sound.
Some languages, including English, have glottal consonants produced only by the glottis, or the vocal cords and the space between them. English has the glottal stop, as noted above, as well as the glottal fricative /h/ as in "hat." Glottal consonants are sometimes considered to be instances of pure phonation rather than true consonants, since other consonants are characterized by a place of articulation such as the lips or the teeth as well as the state of the glottis. Glottal consonants, on the other hand, have no place of articulation other than the glottis.
