In this article, we propose a new method of representing and analyzing music audio records. The method is based on the concept of the trajectory of fifths, which was initially developed for the analysis of music represented in MIDI format. To adapt this concept to the needs of audio signal processing, we implement a short-term spectral analysis of a musical piece, followed by a mapping of its subsequent spectral timeframes onto signatures of fifths reflecting relative intensities of sounds associated with each of the 12 pitch classes. Subsequently, the calculation of the characteristic points of the consecutive signatures of fifths enables the creation of the trajectory of fifths. The results of the experiments and statistical analysis conducted in a set of 8996 audio music pieces belonging to 10 genres indicate that this kind of trajectory, just as its MIDI-compliant precursor, is a source of valuable information (i.e., feature coefficients) concerning the harmonic structure of music, which may find use in audio music classification processes.