Ptolemy's acoustics develops throughout his "Harmonics" chapter 1.3. He defines sound as πάθος άέρος πλησσομέψον, expressing it—as most authors at the time—in terms of a stroke (πληγή), and thus linking the study of sound attributes to that of the strokes. His tripartite analysis of sound stroke represents an original description of sound production by means of an agent (τὸ πλῆττοψ) exciting a medium (τὸ δι' οὗ ἡ πληγή) which, in turn, stimulates the air (τὸ πληττόμεψοψ). However clear Ptolemy's explanation is, a wide consensus on its interpretation has not been reached, since almost each scholar has read Ptolemy's three factors in a different way. As a result, several problems arise in different authors, especially the contradiction between ἡ τοῦ δι' οὗ ἡ πληγὴ σφοδρότης seen as responsible for pitch and ἡ τοῦ πλήττοψτος βία thought of as cause of loudness, but also the understanding of ἡ ἀποχὴ τοῦ πληττομέψον πρὸς τὴψ ἀρχὴψ τῆς κιψήσεως as a differential cause of sounds. This paper tries to settle the aforesaid factors and to clear up the difficulties arising, as well as to comment on some fundamental aspects of Ptolemy's acoustics. [http://www.jstor.org/stable/27736378]