Last month (ahmed) played a four-day residency at Cafe OTO in London that had a truly rapturous finale, and for those who missed it this 5-CD box set of a residency at the Festival For Other Music in Stockholm two years ago offers adequate compensation. Named after the Sudanese-American bassist-oudist-composer Ahmed Abdul-Malik, the quartet has achieved the enviable feat of growing from inside the music of its subject, absorbing its character and synergizing with the strong personalities of the bandmembers, so that pianist Pat Thomas, bassist Joel Grip, drummer Antonin Gerbal and alto saxophonist Seymour Wright push the source material to new musical planes that are nonetheless framed by a limitlessly wide history of black music.

In the epic 45 minute re-imaginings of songs such as ‘African Bossa Nova’ and ‘rooh (the soul)’ there is a subversion of form that makes the original material a rich acorn from which springs the giant beauty of the title, to be possibly interpreted not so much as a towering height that induces an exciting vertigo as a breadth of structural variety that makes the music a thrilling ride. ‘el haris (anxious)’ is arguably a highlight insofar as its evolutionary journey is so fiery. The original crepuscular Arabic motifs morph seamlessly into a range of rhythms that twist through traditions of folk and art music in the 20th century, offsetting the hard edge of the avant-garde with subtleties that are Caribbean as well as African-American.

Most audaciously, there are the strangest collisions of static ragtime and elastic rocksteady that say much of the ability of Wright and Thomas to make a two-beat phrase sing more than one would expect from such a minimal harmonic base. But the whole point, and this really came across at the OTO gigs, is that when the quartet builds up a head of steam, it keeps blowing rather than dropping energy during several changes of pathway, so that the result is tension and increase rather than tension and release.

The trick is to make the next level more daring than the last, and that can involve the further reduction of harmony to one clenched chord that has all the raw, rough, rugged excitation of early blues that is yet to settle into recognised templates, or explosive, hyperactive swing, or, as befits the band’s aesthetic, a crash and mash of the two. Thomas’ hammer of a left hand supersizes the low register to often make the music imperiously bass heavy and enhance the sense of physicality that is upheld by the toughness of the timbres heard elsewhere.

The raucous post-war R&B resonance of the horn, the funky patter of the drums and iron thrust of the double bass combine in a wall of sound that finally tumbles down after a barrage of multi-directional ideas as well as challenges to our perception, or rather assumptions of separateness of different periods of musical history. A single song thus becomes a series of related, unbroken time-stretching events or episodes that reflect a joyously uncompromising ideal in creative music: let a composition undergo transformation by way of the do and dare of improvisation.