Before the beginning of the Mâdhyandinasavana, the noon-oblation, the sacrificer, sitting down behind the Âgnidhrîya altar, and looking towards the north, sings the Sâman, addressed to the Rudras:

In plain words: Before the noon offering begins, the person making the offering sits behind another altar, called the Āgnīdhrīya, faces north, and sings a chant to the Rudras.