Rich and fascinating, the Aka musical tradition is distinguished by the practice of vocal polyphony, which has given rise to important research, in particular by S. Arom and his team [1-4; 8-12]. The musical scales of Central Africa were among them [4-5; 7-9; 11; 14]. However, despite ingenious in situ experiments and an impressive volume of acoustic measurements, the exploration of the Aka musical scale led to an unsatisfactory theoretical compromise. Thus, S. Fürniss presented a scalar system based on a frame of forths compatible with three pentatonic modes and an equipentatonic scale [5-9]. The research presented here takes a new starting point: temporal spectrography [13]. The identification of intervals is based on visual observation of harmonics common to two consecutive or simultaneous sounds [6:401-2]. In addition to the fifth and fourth, whose coincidences are easily identifiable (3 for 2 and 4 for 3), many intervals involving the harmonic 7 have been observed, which has prompted the resumption of research on the basis of "natural" intervals. Several musics were analyzed: monodic singing; voice and instrument (flute, musical bow, harp-zither); vocal polyphony. The analysis method combines sonographic analysis and accurate frequency measurement. An important first result is that the reference to equal temperament and its conversion into cents must be abandoned in favour of another reference: that of the numerical ratio of harmonic numbers. Indeed, the recurring melodic intervals of Aka music are the fourth (4/3), fifth (3/2), major second (9/8), seventh minor (7/4) and three intervals that have no name: 7/6, 8/7, 9/7 [6:407]. Based on new theoretical foundations, our research confirms that Aka pentatonism does not fall within the concept of scale. Rather, it is a system that combines in a variety of ways a group of intervals borrowed from band 6-9 of the harmonic series. The structuring nucleus is the fourth 8/6, which includes only an intermediate sound: the harmonic 7, a remarkable arrangement that is almost inaudible for a Western listener and is at the origin of many difficulties in understanding Aka music. Such a structure favours combinatorics - and therefore the improvisation on which any performance of this music is based - while remaining harmonically coherent.