Bitches Brew, Miles’ best-selling album, still has the ability to mystify even the experienced listener; in its day the double-LP, released in late 1969 and played primarily on rock and underground radio stations, absolutely bewildered jazz critics and divided audiences into pre and post-electronic Miles.

Electronic textures were only half of it, though, and the lesser half at that. What Miles was up to in these ground-breaking adventures was expanding the improvisational palate, extending the nature of rhythmic relationships and, more to the point, time itself.

Augmenting the standard jazz combo with amplified horns, a variety of string instruments, and lots of percussion, Miles instructed his sidemen simply to play what and when they felt like it. Falling between In A Silent Way and A Tribute to Jack Johnson, these sessions mark a major turning paint in Miles’ canon, ushering in a new kind of courage. The idea of experiencing four CDs of improvised madness may strike some reluctant listeners as excessive, but hindsight helps render these experiments more coherently.

Spurred on by the experimental temperament of the 1960s, Miles’ musical consciousness had grown so vast at that point he could encompass the whole, apparent chaos to many, and mold it to his own precise, cutting vision.

Clearly, this is genius at work and a defiantly focused genius at that Miles’ ability to summon the demons of blues, jazz and funk, and make them dance to his tune “Still” is astonishing. Coattail tributes to the electronic Miles may have become fashionable of late, but they can’t touch the real thing. As raw and challenging as when they were recorded, the works contained on these four sides constitute not only essential Miles, but a towering landmark in the evolution of 20th-century musical expression.