The Tunisian musical system is not yet well defined rigorously in terms of its musical scale compared to other modal systems, such as the Turkish and Persian system and now included in the Arab musical system. Given that these last two have known studies which attempt to find theoretical formulas which almost translate the magnitudes of the intervals by semantic signs which correspond to their melodic specificities. Our following study is considered a musicometric specimen to elicit researchers to reveal the nature of Tunisian tbûs (modes). We first approached the theoretical Arab models which refuted the quarter-tone system reported by the modes and rhythms committee of the Arab Music Congress in Cairo in 1932. We have proved, moreover, that through two analyzed examples of the tbâ (mode) dhil, there is no similarity in the quantities of the melodic intervals, in particular the modal notes (sikah « mi half flat», awj « si2 half flat », araq « si1 half flat ») that we were satisfied with in our objective, which evokes the dispute over the referential musical scale of this tbâ and its scalar system.We have mentioned that the musical scale depends on the musician and his interpretation, these cultural tendencies or his usual auditory memory which has influenced his tastes and the musical culture which belongs to him, as well as by the impact of certain factors interpretation. We are ultimately looking to find a very rigorous theoretical model for this tbâ and for the other Tunisian tûbû by introducing artificial intelligence and expanding the number of recordings analyzed which can give us satisfactory results.