- This section treats the distinguishing features of Vedic Sanskrit — see Classical Sanskrit for a general account.
Sound changes between Proto-Indo-Iranian and Vedic Sanskrit include loss of the voiced sibilant z.
Vedic Sanskrit had a bilabial fricative, called upadhmānīya, and a velar fricative, called jihvamuliya. These are both allophones of visarga: upadhmaniya occurs before p and ph, jihvamuliya before k and kh. Vedic also had a retroflex l for retroflex l, an intervocalic allophone of ḍ, represented in Devanagari with the separate symbol ळ and transliterated as ḷ or ḷh. In order to disambiguate vocalic l from retroflex l, ISO 15919 transliterates vocalic l with a ring below the letter, l̥. (Vocalic r is then also represented with a ring, r̥, for consistency and to disambiguate it additionally from the retroflex ṛ and ṛh of some modern Indian languages.)
Vedic Sanskrit had a pitch accent. Since a small number of words in the late pronunciation of Vedic carry the so-called "independent svarita" on a short vowel, one can argue that late Vedic was marginally a tonal language. Note however that in the metrically restored versions of the Rig Veda almost all of the syllables carrying an independent svarita must revert to a sequence of two syllables, the first of which carries an udātta and the second a (so called) dependent svarita. Early Vedic was thus definitely not a tonal language but a pitch accent language. See Vedic accent.
Pāṇini gives accent rules for the spoken language of his (post-Vedic) time, though there is no extant post-Vedic text with accents.
The pluti vowels (trimoraic vowels) were on the verge of becoming phonological during middle Vedic, but disappeared again.
Read more about this topic: Vedic Sanskrit