The sound inventory of Standard Igbo consists of eight vowels, thirty consonants, and two tones, depending somewhat on the analysis. Igbo has only two syllable types: consonant + vowel (the most common syllable type), vowel or syllabic nasal. There are no consonant clusters and no syllable-final consonants.
There are approximately 30 Igbo dialects, some of which are not mutually intelligible. For the most part, however, differences are lexical and phonological (Ethnologue).
The large number of dialects has hindered the development of a standardized spoken and written Igbo. Standard literary Igbo, based on the Owerri and Umuahia dialects, in use since 1962, is not universally accepted by speakers of other dialects.
Standard Igbo aims to include words from other Igbo dialects as well as loanwords from other languages.
Igbo features vowel harmony with two sets of vowels distinguished by pharyngeal cavity size. The latter can be described in terms of advanced tongue root which involves the expansion of the pharyngeal cavity by moving the base of the tongue forward, and sometimes lowering the larynx during the pronunciation of a vowel.
This adds a breathy quality to the vowel. Vowels within a word harmonize which means that all vowels in a word are produced with the root of the tongue either advanced or retracted.