Contemporary ambient music begins with Brian Eno, who laid claim to the term with 1978’s Ambient 1: Music for Airports. But the idea stretches back a century, to Erik Satie’s idea of “furniture music.” And its roots sink deep into electronic music’s mid-century origins, as the advent of oscillators and then synthesizers allowed artists to sculpt sound in ways never before imagined. You can hear ambient’s early stirrings in Daphne Oram’s exploratory work for the BBC Radiophonic Workshop, in which squealing circuits trace the limits of comprehension; you can hear the sound taking shape in the hypnotic repetitions of Steve Reich’s earliest experiments with tape. Groundbreaking synth studies from Suzanne Ciani, Beatriz Ferreyra, and Laurie Spiegel expand upon the otherworldly atmospheres that will become so central to the form. And at the intersection of new music, disco, and post-punk DIY, Arthur Russell’s World of Echo imagined yet another form of proto-ambient music by turning pop songs diffuse as clouds.