Most people think Miles Davis’s career consisted of a series of radical jumps from one style of music to the next. In almost 50 years of constant creative activity, the trumpeter moved from bebop to cool jazz to hard bop to modal jazz to jazz-rock fusion to styles we have yet to dream up names for – and played a significant role in the development of each. But Davis’s stylistic changes actually followed a recurring pattern: Every time his music reached new heights of complexity, he aimed to simplify it again.

As an ambitious if not especially technically endowed young trumpeter, Davis started his career at the top, first with Billy Eckstine’s celebrated big band, then with the flagship ensemble of bebop, Charlie Parker’s quintet. Yet after participating in bebop’s thickest and most baroque era, he became known for the more tranquil brand of music pioneered by his famous “Birth of the Cool” band in 1949.

Likewise, when Davis’s late 1950s quintet with John Coltrane reached a new plateau of harmonic density – Coltrane pushed him into a phase wherein chords were changing with every blink of an eye – he began looking for ways to simplify. His quartet of the mid-1960s with Wayne Shorter and Herbie Hancock played a more open music, largely based on modes and scales rather than chords.

By the end of the decade, Davis was leaning toward the heavy end of the scale once again. His first semi-electric album, 1969’s “In a Silent Way,” was considerably lighter and more melodic than his second, “Bitches Brew,” which launched the fusion movement just a few months later. Live recordings, most still unreleased, from late 1969 and early 1970 show that Davis and his side men were playing harsh, angular music very close to free jazz – their sound, in fact, was decidedly less accessible than that of Ornette Coleman.

The sextet Davis assembled in the fall of 1970 continued to play electric instruments – including, for the first time, Fender bass and Fender Rhodes electric piano – but simplified the style. The only album Davis released between the summer of 1970 and the end of 1971 was “Live-Evil,” which was drawn partly from a mysterious series of performances at the Washington, D.C., club Cellar Door. “The Cellar Door Sessions 1970” (Legacy 93614), a six-CD box set containing six hours of those recordings, has just been released.

The material was recorded in December 1970, when Davis, along with keyboardist Keith Jarrett, bassist Michael Henderson, saxophonist Gary Bartz, drummer Jack De-Johnette, and percussionist Airto Moreira, played four nights at the Cellar Door. On the final night, the quintet added a special guest, British guitarist John McLaughlin, who had already guested on “Silent Way” and “Bitches Brew.”

Fusion at its best, as the music eventually evolved, was highly dependent on complex compositions and instrumental virtuosity. Most of the music on “The Cellar Door Sessions” is simplicity itself. A mere seven compositions account for six hours of music, being played four or five times each over the four nights. For the most part, the soloists just take off on a groove, a minimal blues-based riff, or a bass line. This band wasn’t about melodic standards or master compositions, but about what these six remarkable players could come up with on the spur of the moment while starting with virtually nothing.

Only a few months earlier, Davis was still including a few standards in his shows – “I Fall in Love Too Easily” seems to have been the last holdout. Anything not written specifically for the Cellar Door band would have been unthinkable. The only older piece in the band’s book was Wayne Shorter’s “Sanctuary,” heard only very briefly on “The Cellar Door Sessions.” The closest thing to a Davis standard on “The Cellar Door Sessions” is “It’s About That Time,” which was all of 18 months old, having been recorded for the first time on “In a Silent Way.” Yet the Cellar Door version is something completely different.

This music is so open and free of expectations that it seems to go everywhere at once. For long stretches, the notes go by so slowly you can count them, and the music practically becomes ambient; other passages are thick and teem with life and activity. At times, the blues-funk groove takes over, but there are also four tracks identified only as “Improvisations,” which are the most avant-garde-like pieces here.

Throughout, Davis electronically adjusts his horn sound to make it more compatible with the Fender instruments. In some passages during the Saturday sets, the ear needs a moment to discern whether the guitar-like trumpet or Mr. McLaughlin’s trumpet-like guitar is doing the soloing.

Though Messrs. Jarrett and McLaughlin both went on to become superstars, the biggest star here – apart from the leader – is Mr. Bartz. His playing is constantly inventive, and of the seven players involved, he best exemplifies the Davis ideal of this band; Mr. Bartz plays both the most far-out and most primitive sounds imaginable. On “Inamorata,” for instance, he utilizes avantgarde multiphonics, playing with a split tone in which he seems to be hitting two notes at once. He makes his voice scream along with his alto; I’ve heard Rahsaan Roland Kirk achieve that with the flute, but rarely heard a saxophonist do it.

In his essay in the booklet, Mr. Jarrett – who has very rarely played electric since his stint with Davis – defends this group from the charge that they were “just a funk band.” “Miles wanted a band that could do many things,” he writes. “If Gary, Jack or I had thought we were in a funk band, we would have been undernourished.”

By the time Davis next entered the studio in March 1972, the band’s personnel had almost completely changed, as had its musical director. In the mid-1970s, Davis would create his densest, most impenetrable music ever, a sound built out of the harshest and most severe elements of jazz, rock, and contemporary classical. Nothing could follow that but silence, which is the only thing Davis created for the second half of the decade.

wfriedwald@nysun.com