This translation of the Rambam’s Mishneh Torah, Yesodei Ha-Torah 7:4, appears in Rabbi Aryeh Kaplan, “Meditation and the Bible” (Simon Weiser or Jason Aronson), p. 65.
A prophet cannot prophesy at will. He concentrates his mind, sitting in a good, joyous mood and meditating (hitboded). One cannot attain prophecy when he is depressed or languid, but only when he is in a joyous state.
When they were seeking prophecy, the prophets would therefore have people play music for them. We thus find: "A band of prophets, coming from a high place, led by harp, drum, flute and lyrej and they were prophesying themselves" (I Samuel 10:5). The term "prophesying themselves" (mitnauim) means that they were making use of the prophetic methods in order to receive a prophetic vision.