It is generally agreed that only the obstruents had a contrast between voiceless and voiced forms in Proto-Afroasiatic, whereas continuants were voiceless.
ɪɾ ɪz dʒˈɛnɚɹəli ɐɡɹˈiːd ðæt ˈoʊnli ðɪ əbstɹˈuːnts hæd ɐ kˈɑːntɹæst bᵻtwˌiːn vˈɔɪsləs ænd vˈɔɪst fˈɔːɹmz ɪn pɹˈoʊɾoʊˌæfɹoʊˌeɪsɪˈæɾɪk, wˈɛɹæz kəntˈɪnjuːənts wɜː vˈɔɪsləs.