The basic unit of the Noh music rhythm is a simple eight beat, although variants exist such as six, four and two beat. The eight-beat rhythm is called Yatsu-byōshi, or Ya-hyōshi, (ya/yatsu means eight, and byōshi/hyōshi means rhythm). There are three forms of vocal matching the rhythm(hyōshiai): Hira-nori, Chū-nori and Ō-nori. Allocating syllables to the each of the eight beats of the rhythm according to the rule of the nori is called Yatsu-wari (eighth parts).