Tangerine Dream followed the artistic and commercial breakthrough of Phaedra with an album that presented an even more intense vision of the band's mid-'70s musical direction. Like its predecessor, Rubycon features lengthy tracks where melodic synth lines revolve around a hypnotic latticework of sequencer patterns, further cementing the band's status as linchpins of the Berlin school of electronic music. But instead of four discrete cuts, the album features a single piece, whose two parts each initially filled one LP side. The track floats in with a swirling, ethereal ambience that makes you think the German synth wizards are harking back to their early days—but after a while things start percolating and the sequencer grooves start bouncing off each other in a mesmerizing manner. The second half of the piece has a slow build as well; after working its way up to a boil, it gradually starts to ease back down, ending the album not with an exclamation point but with an intriguing series of aural question marks.