Released in 1978, Ambient 1: Music for Airports is the record where Brian Eno named and defined ambient music: sound meant to be "as ignorable as it is interesting," written to calm the nerves of people waiting in a terminal. Four long pieces are built from slow, overlapping tape loops of piano, wordless voices and synthesizer, each phrase drifting in and out of phase so the music never quite repeats. "1/1," with Robert Wyatt among the pianists, is the one everyone knows, while "2/1" and "1/2" float on layered choral tones. A quiet cornerstone of electronic music, and a record that rewards both close listening and none at all.