no phonemic contrast between [p] and [f] or [b] and [v]. In Cushitic, the Ethiopian Semitic language Tigrinya, and some Chadic languages, there is no underlying phoneme [p] at all. All or most branches of AA have a contrast between voiceless, voiced, and "emphatic" consonants.] and d is [], ṯ is [] and ḏ is []).}} The emphatic consonants are typically formed deeper in the throat than the others; they can be realized variously as glottalized, pharyngealized, uvularized, ejective, and/or implosive consonants in the different branches. It is generally agreed that only the obstruents had a contrast between voiceless and voiced forms in Proto-Afroasiatic, whereas continuants were voiceless. Vowel systems There is a large variety of vocalic systems in AA. All branches of Afroasiatic have a limited number of underlying vowels (between two and seven), but the number of phonetic vowels can be much larger. The quality of the underlying vowels varies considerably by language; the most common vowel throughout AA is schwa. In the different languages, central vowels are often inserted to break up consonant clusters (a form of epenthesis). Attempts to reconstruct the vocalic system of Proto-Afroasiatic vary considerably. Igor M. Diakonoff proposed that Proto-AA had a three vowel system of long and short a, i, and u. Christopher Ehret proposed a five vowel system with long and short a, e, o, i, and u. Vladimir Orel and Olga Stolbova instead proposed a six vowel system with a, e, o, i, ü ([]), and u. Ronny Meyer and H. Ekkehard Wolff instead propose that Proto-Afroasiatic may have had no vowels as such, instead employing various syllabic consonants (*l, *m, *n, *r) and semivowels or semivowel-like consonants (*w, *y, *ʔ, *ḥ, *ʕ, *h, *ʔʷ, *ḥʷ, *ʕʷ, *hʷ) to form syllables. Tones The majority of AA languages are tonal languages: phonemic tonality is found in Omotic, Chadic, and Cushitic languages, but absent in Berber and Semitic. There is no information on whether Egyptian had tones. In contemporary Omotic, Chadic, and Cushitic languages, tone is primarily a grammatical feature: it encodes various grammatical functions, only differentiating lexical roots in a few cases. In most Cushitic languages, not every not every syllable has to have a tone, whereas in Chadic and some Omotic languages, every syllable does. Some scholars postulate that Proto-Afroasiatic was a tonal language, with tonality subsequently lost in some branches: Christopher Ehret has postulated a tonal system of at