FWIW, the first sound of Rgveda is 'a' (*short* a-sound):
agnim iiLe purohitaM, yajñasya devam RtvijaM hotaaraM ratnadhaatamam. The first line contains the following vowels: a, i, ii (long i-sound), e, u, o , i, a. Please, look at the devanaagarii alphabet here, especially 'VOWELS - FULL FORM': http://sanskrit.farfromreal.com/index.php?x=writ_alpha If we ignore the long vowels, most of them are included in the first line: a, i, u, e (sandhi of a + i), o (sandhi of a + u) Those not included are: R (vocalic r-sound), L (vocalic l-sound, quite rare) and diphthongs 'ai' (diachronically aa + i, methinks) and 'au' (aa + u).
