Avestan phonology

This article deals with the phonology of the Avestan language. Avestan is distinguished among the Indo-Iranian languages by having retained voiced sibilants, and having fricative rather than aspirate series.

Consonants
According to Beekes, and  are allophones of /θ/ and /x/ respectively.

š versus rt
Avestan š continues Indo-Iranian *-rt-. Its phonetic value and its phonological status (one or two phonemes) are somewhat unclear. The conditions under which change from -rt- to -š- occurs are fundamentally ill-defined. So, for example, ərəta/arəta (Gathic/Younger) "establish" is a variant of aša but is consistently written with /r t/. Similarly, arəti "portion, allot" and aši "recompense." But aməša "immortal" is consistently written with /š/, while marəta "mortal" is consistently written with /r t/. In some instances a change is only evident in Younger Avestan. For example, the Gathic Avestan word for "bridge" is pərətūm, while in Younger Avestan it is pəšūm. Both are singular accusative forms, but when the word is singular nominative the Younger Avestan variant is again (and all but once) with /r t/.

Benveniste suggested š was only a convenient way of writing /rt/ and should not be considered phonetically relevant. According to Gray, š is a misreading, representing /r r/, of uncertain phonetic value but "probably" representing a voiceless r.

Miller follows the older suggestion that Avestan š represents a phoneme of its own, for which he introduces the symbol "/Ř/" and identifies phonetically as  (the voiceless allophone of Czech ř). He goes on to suggest that in writing, -rt- was restored when a scribe was aware of a morpheme boundary between the /r/ and /t/.

Transcription
There are various conventions for transliteration of Dīn Dabireh. We adopt the following one here. Vowels:

Consonants:

The glides y and w are often transcribed as ii and uu, imitating Dīn Dabireh orthography. The letter transcribed  indicates an allophone of with no audible release at the end of a word and before certain obstruents.