The Cheyenne language is a Native American language spoken in present-day Montana and Oklahoma, USA. It is part of the Algonquian language family. Like many Native American languages, it has complex agglutinative morphology.

Phonology

Cheyenne phonology is not exceptionally complex. While there are only three basic vowels, they can be pronounced in three ways: high pitch, low pitch, and voiceless[1]. The high and low pitches are phonemic, while vowel devoicing is governed by environmental rules, making voiceless vowels allophones of the voiced vowels. The digraph ‘ts’ represents assibilated /t/; a phonological rule of Cheyenne is that underlying /t/ becomes assibiliated before an /e/ (t > ts / __e). Therefore, ‘ts’ is not a separate phoneme, but an allophone of /t/.

The standard Cheyenne orthography is neither a pure phonemic system nor a phonetic transcription; it is, in the words of linguist Wayne Leman, a "pronunciation orthography." In other words, it is a practical spelling system designed to facilitate proper pronunciation. Some allophonic variants, such as voiceless vowels, are shown.
Consonants
  bilabial dental palatal velar glottal
stop p t   k ?
fricative v s S x h
nasal m n      
Vowels
  front central back
non-low e   o
low   a  

[1] There are also three other variants of the phonemic pitches: the mid, raised-high and hanging-low pitches. These are often not represented in writing, although there are standard diacritics to indicate all of them.

Reference