A tone smoothing is performed such that to each time section of a melody line segment a number is associated such that for all groups of directly neighboring time sections, to which the same spectral component is associated by the melody line segment, the numbers associated with the directly neighboring time sections are different numbers from one to the number of the directly neighboring time sections, for each spectral component that is associated with one of the time sections of the melody line segment, the numbers of those groups are added up to which time sections of the same the respective spectral component is associated by the melody line segment, a smoothing spectral component is determined as the spectral component for which the greatest summing-up results, and the melody line segment is changed, by associating the determined smoothing spectral component to each time section of the melody line segment. By this, in particular the inadequacy of monophonic audio signals is considered, usually comprising a transient process at beginnings of notes, so that only to the end of the notes the desired note pitch is achieved.