Assamese phonology

Phonology
The Assamese phonemic inventory consists of eight vowels, ten diphthongs, and twenty-one consonants.

Alveolar stops
The Assamese phoneme inventory is unique in the Indic group of languages in its lack of a dental-retroflex distinction among the coronal stops. Historically, the dental and retroflex series merged into alveolar stops. This makes Assamese resemble non-Indic languages of Northeast India (such as languages from the Austroasiatic and Sino-Tibetan languages). The only other language to have fronted retroflex stops into alveolars is the closely related eastern dialects of Bengali (although a contrast with dental stops remains in those dialects). Note that /r/ is normally realized as [ɹ] or as a retroflex approximant.

Voiceless velar fricative
Assamese and Sylheti are unusual among Eastern Indo-Aryan languages for the presence of the or, historically the MIA sibilant has lenited to /x/ and /h/ (non-initially). The derivation of the velar fricative from the coronal sibilant is evident in the name of the language in Assamese; some Assamese prefer to write $\langleOxomiya\rangle$ or $\langleÔxômiya\rangle$ instead of $\langleAsomiya\rangle$ or $\langleAsamiya\rangle$ to reflect the sound change. The voiceless velar fricative is absent in the West Goalpariya dialect as against wide usage in Eastern dialects.

Assamese is called "Axamiyaa" in the Assamese language. The /x/ there represents the phoneme similar to the variety, which is present in many European Indo-European languages, like sound of 'X' in Greek Xeros (dry), 'ch' of Loch (Lake) Scottish, Bach, Ulrich (proper nouns) in German etc. Apart from Assamese and Sylheti this sound is not to be found in any of the standard Indian languages.

Velar nasal
Assamese and Bengali, in contrast to other Indo-Aryan languages, use the velar nasal (the English ng in sing) extensively. In many languages, while the velar nasal is commonly restricted to preceding velar sounds, in Assamese it can occur intervocalically. This is another feature it shares with other languages of Northeast India, though in Assamese the velar nasal never occurs word-initially.

Vowel inventory
Eastern Indic languages like Assamese, Bengali, Sylheti, and Oriya do not have a vowel length distinction, but have a wide set of back rounded vowels. In the case of Assamese, there are four back rounded vowels that contrast phonemically, as demonstrated by the minimal set: কলা kôla ('deaf'), ক'লা kola  ('black'), কোলা kûla  ('lap'), and কুলা kula  ('winnowing fan'). The high-mid back rounded vowel is unique in this branch of the language family.