This is analogous to the direct–oblique distinction in proto-Pamir, but with the split conditioned by voice rather than by tense.
ðɪs ɪz ɐnˈæləɡəs tə ðə dᵻɹˈɛkt oʊblˈiːk dɪstˈɪŋkʃən ɪn pɹˈoʊɾoʊpˈæmɪɹ, bˌʌt wɪððə splˈɪt kəndˈɪʃənd baɪ vˈɔɪs ɹˈæðɚ ðɐn baɪ tˈɛns.