VOICELESS ASPIRATED ALVEOLAR STOP [tʰ]
VOICELESS ALVEOLAR FRICATIVE [θ]
Tav with dagesh is pronounced similarly to English "t", except the tip of the tongue is placed behind the teeth on the gums instead of on the teeth themselves. Tav with rafe, which typically occurs after vowels, is pronounced with the tip of the tongue in the same place (i.e., on the gums behind the teeth), but with an allowance of air to pass through to make a fricative sound.
SOURCES AND FURTHER READING
Khan, Geoffrey. 2020. The Tiberian Pronunciation Tradition of Biblical Hebrew. Cambridge: Cambridge and Open Book Publishers. §I.1.23.