Ptolemy's acoustics develops throughout his Harmonics chapter 1.3. He defines sound as παος αερος πλησσομενου, expressing it—as most authors at the time—in terms of a stroke (πληγη), 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 (το πληττον) exciting a medium (το δι' ου η πληγη) which, in turn, stimulates the air (το πληττομενον). 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 η του δι' ου η πληγη σοδροτης seen as responsible for pitch and η του πληττοντος βια thought of as cause of loudness, but also the understanding of η αποχη του πληττομενου προς την αρχην της κινησεως 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.