In recent years, the long-standing Swedish imprint, Caprice, has joined forces with the curatorial vision of saxophonist Mats Gustafsson and Roger Bergner of the Centre for Swedish Folk Music & Jazz Research, producing the truly incredible Öppet series, focusing on under-celebrated Scandinavian creative, experimental music from the 1960s and 70s. Now they're back with the fourth installment in the series, Fyra, dedicated to the Norwegian vocalist Karin Krog.

Across the 1960s and 70s Krog worked at the centre of the context of radical music that bridged both sides of the Atlantic, working with the likes of Dexter Gordon, Archie Shepp and John Surman, among others, as well as making a singular body of experimental work, inspired by the innovations of John Cage and Arne Nordheim, processing her vocals with electronics. Fyra gathers two revelatory and previously unreleased bodies of recordings made in 1970 at the studios of the North German radio and television broadcaster, NDR, the first featuring Krog working in a septet alongside Lars-Göran Ulander on alto sax & flute, Calle Neumann on alto sax & flute, Berndt Egerbladh on piano & organ, Terje Rypdal on electric guitar, Niels-Henning Ørsted Pedersen on bass, and Sten Öberg on drums, while the second comprises stunning duos between Krog, on vocals & electronics, and the legendary Swiss percussionist and drummer Pierre Favre.

Opening with the reasonably long-form track, Arcticness, the group settles into languid, medium paced pulses and grooves, flirting at the borders of post-bop and spiritual jazz, leaving plenty of space for Krog's brilliant interventions, treating her voice like an instrument rather than a means to deliver lyrical meaning. From here the group moves into increasingly fascinating waters, fully taking off on the second side into some seriously brilliant free jazz fire, bookended by slow paced balladic moments.

As Krog's sessions at NDR with this brilliant septet close, she enters into a duo with Pierre Favre, live processing her vocals with electronics over three mind-blowing tracks. Stripped back to the minimal of means, Favre's delicate clatter on percussion met with bubbling phonics and momentary poetics from Krog, at each turn and evolution the pair are locked in, immersed in a knotted web of sonority that remains engrossing and strikingly contemporary, more than 50 years since it was laid to tape.

Issued by Caprice in a stunning vinyl edition, complete with extensive liner notes by both Mats Gustafsson and Krog.