The relationship between parameters extracted from the musical stimuli and emotional response has been traditionally approached using several physical measures extracted from time or frequency domains. From time-domain measures, the musical onset is defined as the moment in that any musical instrument or human voice issues a musical note. The onsets’ sequence in the performance of a specific musical score creates what is known as the onset curve (OC). The influence of the structure of OC on the emotional judgment of people is not known. To this end, we have applied principal component analysis on a complete set of variables extracted from the OC to capture their statistical structure. We have found a trifactorial structure related to activation and valence dimensions of emotional judgment. The structure has been cross-validated using different participants and stimuli. In this way, we propose the factorial scores of the OC as a reliable and relevant piece of information to predict the emotional judgment of music.