This phrase is taken from The Fellowship of the Ring, book II, chapter 1 (page 261):
At first the beauty of the melodies and of the interwoven words in elven-tongues, even though he understood them little, held him in a spell, as soon as he began to attend to them. Almost it seemed that the words took shape, and visions of far lands and bright things that he had never yet imagined opened out before him; and the firelit hall became like a golden mist above seas of foam that sighed upon the margins of the world. Then the enchantment became more and more dreamlike, until he felt that an endless river of swelling gold and silver was flowing over him, too multitudinous for its pattern to be comprehended; it became part of the throbbing air about him, and it drenched and drowned him.
What does "the throbbing air about him" mean?