This proposal aims to analyse the element that characterized the third period of Giacinto Scelsi: the ‘sola nota’. ‘Sola nota’ is the artifice that allowed the composer to focus its work on specific areas of ‘Klang’. Scelsi composed and de-composed the sound through the mutual interaction of notes, frequencies used to create a compound. Despite its complexity, the ‘sola nota’ always leads to the idea of a unity in a state of vibration. In this lecture the particular use of notation techniques to create the ‘sola nota’ and to ‘write’ the characteristic Scelsi’s sound will be shown. The analytical model adopted provides for the identification of specific microtonal areas prescribed by the score. The examples given are taken from some of the most important Scelsi’s compositions: Pfhat, Xnoybis and the cycle of the Quattro Pezzi per Orchestra. Furthermore, it will be possible to detect how tensions between microtonal areas allow to draw a macro-structure for the composition. This work is part of a PhD research focused on the controversial relationship between Scelsi and his main collaborator Vieri Tosatti, the ‘craftsman’who created the most important Scelsi’s scores.