As we learn on this six-CD collection, Miles Davis and John Coltrane's many brilliant moments together were not created in a vacuum; they were not instant genius at the depression of a trumpet valve or sax key. These were works in progress with false starts, alternative takes and improvisations in the studio. Over four tracks on disc two, for example, Davis plays three versions of "Sweet Sue, Just You." The tune morphs from a simple story with basic chord changes to a final version in which each musician's solo incorporates these chord changes in patterns that hardly recall the melody. Every noise, it seems, has been duly documented.

An added value is the opportunity to hear Coltrane when he was just beginning to reach for some distant, unexplored shore of sound. Contrast the Coltrane solos on "Round Midnight" (disc two) and "Straight, No Chaser" (disc three), which were recorded two years apart: They sound as if they were played by two different men. After all, by the time of the Thelonious Monk recording, Coltrane had left the Davis quintet, kicked his heroin habit, married, gigged with Monk, embarked on his spiritual journey and begun to think in a new modal and rhythmic form, which became known simply as Coltrane's sheets of sound.

Coltrane's second employment with the Davis quintet helped produce the Milestones and Kind of Blue sessions. The latter was a real breakthrough, particularly on "Flamenco Sketches" (disc four). Davis envisioned the composition as a series of scales, each to be played as long as the soloist wished, until he had completed the series. There were six takes of "Flamenco Sketches" performed in the studio on April 22, 1959. The box includes the album version and an earlier, unspecified cut. Even from this limited perspective of the tune's evolution, you can hear how each musician analyzed his solo, then redefined it in terms of the overall piece. Obviously, all six takes of "Flamenco Sketches" would've been fine.

As a bandleader, Davis would constantly exhort his musicians to define their playing. He repeatedly told his sidemen to play what they heard, not what they had learned. He introduced the story and then let each soloist create a chapter that added to the tension. Coltrane fit well into this setting, which is probably why Davis admired him. No Coltrane solo was ever predictable; you never knew where his chapter would take you.

This boxed set isn't cheap. You can pass if you already own Milestones, Kind of Blue and Round About Midnight. Yet if you really love the inner mechanisms of jazz, and money isn't an issue, there's no question you have to own this box.