Proto-Indo-Iranian descriptive phonology

In addition to the vowels, *H, and *r̥ could function as the syllabic core.

Two palatal series
Proto-Indo-Iranian is hypothesized to contain two series of stops or affricates in the palatal to postalveolar region. The phonetic nature of this contrast is not clear, and hence they are usually referred to as the "primary"/"first" series (*ĉ *ĵ *ĵʰ, continuing Proto-Indo-European palatovelar *ḱ *ǵ *ǵʰ) and the "second(ary)" series (*č *ǰ *ǰʰ, continuing Proto-Indo-European plain and labialized velars *k⁽ʷ⁾ *g⁽ʷ⁾ *gʰ⁽ʷ⁾ in palatalizing contexts). The following table shows the most common reflexes of the two series (Proto-Iranian is the hypothetical ancestor to the Iranian languages, including Avestan and Old Persian):

Laryngeal
Proto-Indo-European is usually hypothesized to have had three to four laryngeal consonants, each of which could occur in either syllabic or non-syllabic position. In Proto-Indo-Iranian, the laryngeals merged as one phoneme /*H/. Beekes suggests that some instances of this /*H/ survived into Avestan as unwritten glottal stops.

Accent
Like Proto-Indo-European and Vedic Sanskrit (and also Avestan, though it was not written down ), Proto-Indo-Iranian had a pitch accent, indicated by an acute accent over the accented vowel.