The genre that Brian Eno famously said should be “as ignorable as it is interesting” has taken more forms than even that restless philosopher/soundscaper might have expected. With roots in Satie’s 19th-century “furniture music” and Terry Riley’s ’60s minimalism, ambient can encompass the pulsing synth experiments of Tangerine Dream, the beatific new age of Laraaji, and the quietly mind-bending analog miniatures of Aphex Twin. From field recordings to full-throttle drone music, ambient music is as varied as the spaces it is created to fill; a dream made of moving air, it might be psychedelic music’s purest form.