Establishing a phoneme inventory for Rau is difficult, given the complex phonetic alternations and the dialectal diversity. Rau has numerous dialects, each of which has a slightly different phonology. The Rau covered in this grammar is slightly artificial, with the consonantism of the conservative inland dialect of Zamúg and the vocalism found in the more populous eastern reaches of the Rau heartland, including the capital city of Bâkhton. Rau dialects are generally mutually intelligible; the main differences are in the vowels and the voiced plosives.
/p b d̪ t dz k g q ɢ/ <p b d t z k g q r>
/ɬ s ʃ x χ/ <l s sh kh h>
/m n ŋ/ <m n ng>
/ʇ ᵑʇ ᶢʇ/ <c nc gc>
/ǁ ᵑǁ ᶢǁ/ <x nx gx>
/ǂ ᵑǂ ᶢǂ/ <ç nç gç>
/ɬ/ ranges from [ɬ~θ~t̪θ~t̪~f] in the various dialects; the value given here is the most common in Bâkhton.
/x/ becomes [f] before rounded vowels in some dialects.
The /d̪ t dz/ imbalance is addressed in various ways. Bâkhton is conservative here, but younger speakers may adopt the shift of ɬ > t̪ from the far-eastern dialects. Western dialects often have t dz > t̪ dʒ; far eastern dialects merge t dz to ɾ in most positions, but preserve dz as [z] where lenition is blocked.
/ɢ/ is almost always realized as [ʁ], even in dialects that have no other lenition of the voiced plosives.
Many dialects have /j w/.
Voiced plosives in Bâkhton
Exceptionally difficult; write up later.
The maximal short vowel system is /a ɒ e ʌ o i ɯ/. Notable features of various dialects:
- Merger of /a ɒ/, or failure to develop the split in the first place
- ɒ o > o u
- Merger of /ʌ ɯ/
Bâkhton is relatively conservative here: older speakers have none of these traits. Younger speakers, howver, typically show merger of ʌ ɯ, to ɯ before coronals and ʌ otherwise.
- The contrast between /ʌ/ and /ɯ/, generally an eastern innovation
- The merger of /ɒ/ and /a/, generally a western innovation but also present in the far east
- The treatment of *[ð]: [ð], [d], [z], or 
- T-flapping, probably introduced through contact with Narng
- Syllabification of voiced plosives
- Lenition of coda voiced plosives; certain dialects, especially in the far east, have lost voiced plosives entirely, and must now be analyzed as having contrastive vowel lengdth
- /j w/, introduced in various places through loanwords but predictable and non-phonemic in the Rau heartland