The supra-laryngeal vocal tract includes the larynx, the epiglottis, the pharynx, the oral cavity, and the nasal cavity, which constitute [[articulatory system]]. The supra-laryngeal vocal tract measures around 17 cm for male voices. Female voices have, on average, a smaller vocal tract length. Humans can modify the shape of the supra-laryngeal vocal tract, including the opening of the nasal cavity, to modify the sound produced by the [[glottal airflow velocity]] passing through it. The sounds of the [[speech signal]] modified by the supra-laryngeal vocal tract can be classified according to the [[manner of articulation]] or the [[place of articulation]]