SHORT FRONT OPEN UNROUNDED VOWEL [a]
Tiberian Hebrew vocalic shewa—vocalic shewa means it is pronounced as a vowel, as opposed to silent shewa, which merely closes a syllable—is normally pronounced as a short a-vowel in the front of the mouth just like pataḥ.
SHORT ASSIMILATED VOWEL [a], [ɔ], [ɛ], [e], [i], [o], [u]
Before a guttural consonant (אהחע), shewa is pronounced with the same vowel quality as that of the guttural.
SHORT FRONT CLOSED UNROUNDED VOWEL [i]
Before the consonant yodh, Tiberian Hebrew shewa is pronounced a short i‑vowel.
SOURCES AND FURTHER READING
Khan, Geoffrey. 2020. The Tiberian Pronunciation Tradition of Biblical Hebrew. Cambridge: Cambridge and Open Book Publishers. §I.2.5.