“These musicians had a rare empathy and sense of exploration. At one point it feels like they’re going to collectively take off”: Tangerine Dream’s Rubycon box set

The most effective way into Tangerine Dream’s five-CD box set is to start with the four live CDs. They were essentially an improvisation trio, and founder Edgar Froese said he sought “transparency” in their music. Although that idea was never fully explained, it was realised in Rubycon’s spatial ambience and panoramic spread.

The album was originally released in March 1975, and the live recordings here come from London’s Rainbow Theatre in October 1974 and the Royal Albert Hall in April 1975 (with Michael Hoenig depping for Peter Baumann).

The excitement generated by 1974’s breakthrough album Phaedra is reflected in compère John Peel’s introduction at the Rainbow. Tangerine Dream’s soundworld must have sounded thrillingly new: a kaleidoscopic combination of Baumann’s synths and electric piano; Froese’s Mellotron, synth and occasional guitar; and Chris Franke’s double Moog with sequencers.

At 36 minutes, the first part of the Rainbow concert is longer than Rubycon in its entirety. Group improvisation inevitably gives rise to longueurs, but these musicians had a rare empathy and sense of exploration. At one point it feels like they’re going to collectively take off, but they veer into abstract, harpsichord-like plucks and twangs.

The sequencer pulses often have less of the smooth dancing flow than on the studio recording, and while there are some lush sonic drifts, it can also become unsettling – particularly when Froese barks out dissonant fanfares.

Part One opens with tentative electric piano, then a heavenly Mellotron choir ushers a luminous section that ebbs and flows, topped with soaring synths. A bonus Steven Wilson remix of the original 15-minute take of this intro shows it was edited for release, coming in at the point when it really starts to happen. Sequencers travel through swirling electronic textures and snatches of melody, including dramatic reverse-echoed prepared piano chords.

Part Two opens with Mellotron and Baumann’s voice in an eerie wind tunnel of sound – surely inspired by György Ligeti’s choral work Lux Aeterna – followed by another sequencer section, which dissolves into heavily-phased field recordings of the sea. Dissonant organ chords gently throb, and wisps of Mellotron and synth draw the album to a poignant conclusion.

Rubycon reached No.10 in the UK Charts in 1975, and though perfectly formed, at a mere 35 minutes it feels a bit on the short side. For anyone who always wanted more, there’s plenty on offer here.

Rubycon: 50th Anniversay Edition is on sale now via Reactive.