भिव्याहरति यर्क्तत्साम तस्मादप्राणन्ननपानन्साम गायति यत्साम स उद्गीथस्तस्मादप्राणन्नपानन्नुद्गायति ॥ ४ ॥
In plain words
...articulates fully—that is the sāman. Therefore, without exhalation or inhalation, he sings the sāman. What is the sāman is the udgītha; therefore, without exhalation or inhalation, he chants the udgītha.
Close to the Sanskrit
...fully articulates, that is the sāman; therefore without exhaling and without inhaling he sings the sāman. That which is the sāman, that is the udgītha; therefore without exhaling and without inhaling he chants the udgītha.