Nasalization refers to whether some of the air escapes through the nose. In nasal vowels, the velum is lowered, and some air travels through the nasal cavity as well as the mouth. An oral vowel is a vowel in which all air escapes through the mouth. French, Polish and Portuguese contrast nasal and oral vowels.
Voicing describes whether the vocal cords are vibrating during the articulation of a vowel. Most languages only have voiced vowels, but several Native American languages, such as Cheyenne and Totonac, contrast voiced and devoiced vowels. Vowels are devoiced in whispered speech. In Japanese and Quebec French, vowels that are between voiceless consonants are often devoiced.
Modal voice, creaky voice, and breathy voice (murmured vowels) are phonation types that are used contrastively in some languages. Often, these co-occur with tone or stress distinctions; in the Mon language, vowels pronounced in the high tone are also produced with creaky voice. In cases like this, it can be unclear whether it is the tone, the voicing type, or the pairing of the two that is being used for phonemic contrast. This combination of phonetic cues (i.e. phonation, tone, stress) is known as register or register complex.
Advanced tongue root (ATR) is a feature common across much of Africa. The contrast between advanced and retracted tongue root resembles the tense/lax contrast acoustically, but they are articulated differently. ATR vowels involve noticeable tension in the vocal tract.