There’s been plenty of bootlegged material over the years from this celebrated 1961 tour by John Coltrane with saxophonist and bass clarinetist Eric Dolphy, a similarly single-minded seeker, as guest artist. Now Acrobat has remastered tapes from six shows in Paris, Copenhagen, Helsinki and Stockholm and pulled them into a useful four-disc set, with a typically authoritative guiding overview from saxist/writer Simon Spillett. Coltrane had not long formed his “classic” quartet with pianist McCoy Tyner, bassist Jimmy Garrison and drummer Elvin Jones, and in 1961 had also forged a brief but creative association with Dolphy. Their fearless stretching of the postbop envelope remains enthralling (at times even shocking) in its intensity, and the set pinpoints how the same pieces (including Blue Train, Impressions, My Favourite Things and Naima) change from night to night. There’s a swooping Dolphy bass clarinet performance on Naima in Copenhagen, and fascinating contrasts between Coltrane’s seamlessly wailing tenor sound and Dolphy’s more angular, wriggling alto on the second Helsinki version of Impressions. Acoustics are inevitably uneven, but students of Coltrane’s gamechanging work at a conceptual turning point won’t mind that.