Ambient music used to be simple. As on the pioneering Brian Eno records of the early '80s, most of it consisted of a steady electronic stream of burps and bleeps over a subtle (or nonexistent) rhythmic bed. The music traversed that ultrathin line between being innovative and yet utterly banal, and you either loved it or hated it for that quality.
Ambient is no longer an underground phenomenon. Two years ago, the French Musical duo known as Deep Forest merged easy-listening ambient ooze with Pygmy chanting. Called Deep Forest, the album meditative music for the media-overload age became a left-field cult hit. It demonstrated the genre isn't a musical dead-end street, while pinpointing the conundrum of ambient music in the '90s: How do you continue to make intentionally boring chill-out music interesting?
The most bare-bones side of ambient thrives in the Black Dog, a British multimedia collective. Their first major-label album, Spanners, is a series of antiseptic, hypnosis-inducing machine burbles, but with just the right amount of jarring elements to keep listeners awake. There's a moment in ''Psil-Cosyin,'' for instance, that sounds like a robot getting whipped, while the androidal panting on ''Further Harm'' is as sexy as ambient gets. B+