At the same time, arranger Gil Evans began hosting informal salons at his apartment, located on 55th Street in Manhattan, three blocks away from the jazz nightclubs of 52nd Street. Evans had gained a reputation in the jazz world for his orchestration of bebop tunes for the Claude Thornhill orchestra in the mid-1940s. Keeping an open door policy, Evans's apartment came to host many of the young jazz artists of late-1940s New York. The salon featured discussions about the future of jazz, including a proposed group with a new sound. According to jazz historian Ted Gioia:
[The salon members] were developing a range of tools that would change the sound of contemporary music. In their work together, they relied on a rich palette of harmonies, many of them drawn from European impressionist composers. They explored new instrumental textures, preferring to blend the voices of the horns like a choir rather than pit them against each other as the big bands had traditionally done with their thrusting and parrying sections. They brought down the tempos of their music . . . they adopted a more lyrical approach to improvisation . . .Davis' nonet
While Evans had originally hoped to work with Charlie Parker on this project, Evans felt that Parker was too dedicated to his own solo voice and not an ensemble sound that Evans was hoping to tap into. With Parker out of the picture, Davis took the lead on the project; Davis and Evans met in the summer of 1947, discovering a mutual respect for each other's work. The two men decided to tap into the members of the salon to for the new group, this group eventually becoming the Miles Davis Nonet. Salon member, arranger, and baritone saxophonist Gerry Mulligan joined the project, having previously written for Gene Krupa's orchestra, as it was felt he could bring a lighter sound that Davis and Evans were looking for.
The members of the salon came to the conclusion that the ensemble should feature two saxophones, four brass, and rhythm section for a total of nine players. Evans and Mulligan spent the winter working out instrumentation, augmenting the traditional bop quintet of saxophone (in this case, alto saxophone), trumpet, and rhythm section, with baritone saxophone, trombone, French horn, and tuba. The two men looked to create pairings within the ensemble, Mulligan stating: "We picked instruments [with matching timbres] . . . and one of each. We had a high section with a trumpet and the alto, we had a middle section with the trombone and the French horn, and a low section with the baritone and tuba. So we had those . . . basic colors to work with." The omission of tenor saxophone was seen as highly unusual, as it was seen as one of the standard jazz instruments.
Davis, Evans, and Mulligan then went about assembling the members of the nonet, Davis and Mulligan taking trumpet and baritone saxophone respectively. For alto saxophone, Davis originally wanted Sonny Stitt for the part, but it was decided that Stitt's sound, much like Parkers, was too bop for what the nonet was pursuing. On Gerry Mulligan's suggestion, Davis asked salon member Lee Konitz to join the group. Konitz had played with Mulligan in Claude Thornhill's orchestra, and was seen by some as a stylistic alternative to Parker, with much a lighter and airier sound. Tuba player Bill Barber and French hornist Sandy Siegelstein came to the nonet via the brass section of the Thornhill band, Siegelstein to be later replaced by Junior Collins. Trombonist and salon member J. J. Johnson was the first choice for the band, but due to engagements with the Illinois Jacquet band could not originally play with the nonet, though he was able to record with the group on the final two sessions. Both bassist Al McKibbon and pianist and arranger John Lewis had known Davis as members of Dizzy Gillespie's orchestra. Drummer Max Roach had been a member of Parker's quintet with Davis and was a natural choice for the nonet due to his enthusiastic engagement in the ideals of the salon.
Davis was able to secure a two-week engagement in September 1948 for the nonet opening for Count Basie at the Royal Roost in New York. For the bands book, Mulligan contributed six arrangements, Lewis three, Evans two, and composer John Carisi arranged his own composition, "Israel", for the band. On Davis's insistence, a sign was placed outside the Roost advertised, "Arrangements by Gerry Mulligan, Gil Evans, and John Lewis," an unusual advertisement that highlighted the collaborative nature of the venture. The band played at the roost for the weeks of August 30, to September 4, and September 13, to September 18,. For these live dates Mike Zwerin played trombone and former Dizzy Gillespie vocalist Kenny Hagood sang on "Darn That Dream" and "Why Do I Love You". There was a further short residency the following year at the Clique Club, these three sets making up the nonet's only live appearances. Arranger and Capitol Records talent scout Pete Rugolo heard the nonet at the Royal Roost and offered the nonet a chance to make a record
The nonet recorded twelve tracks for Capitol during three sessions over the course of nearly a year and a half. Davis, Konitz, Mulligan and Barber were the only musicians who played on all three sessions, though the instrumental lineup was constant (excepting the omission of piano on a few songs and the addition of Hagood on "Darn That Dream"). The first session occurred on January 21, 1949, recording four tracks: Mulligan's "Jeru" and "Godchild" as well as Lewis's "Move" and "Budo". Jazz critic Richard Cook hypothesizes that Capitol, wanting to get a good start, recorded these numbers first because they were the most catchy tunes in the nonet's small repertoire. That date Kai Winding replaced Zwerin on trombone, Al Haig replaced Lewis on piano, and Joe Shulman replaced McKibbon on bass.
The second recording date came three months later on April 22, 1949, Davis filling in for Fats Navarro in Tadd Dameron's band with Charlie Parker during the interim. The band returned to the studio with five substitutions in personnel: J. J. Johnson on trombone, Sandy Siegelstein on French horn, Nelson Boyd on bass, and Kenny Clarke on drums, and John Lewis returning to piano. At this session the nonet recorded Mulligan's "Venus De Milo", Lewis's "Rogue", Carisi's "Israel", and "Boplicity", a collaboration between Davis and Evans, credited to the pseudonym "Cleo Henry".
The band did not return to the studio again until March 9, 1950. Davis did not call the band for any rehearsals or live performances between the second and third recording dates. The March 1950 date featured Mulligan's "Darn That Dream", "Rocker", and "Deception", and Evans's arrangement of Chummy MacGregor's "Moon Dreams", which had been released in a jazz arrangement by Glenn Miller and the AAF Band in 1944 on V-Disc. The band saw more substitutions, with Gunther Schuller on French horn and Al McKibbon on bass. Kenny Hagood returned for vocals on "Darn That Dream".
One of the features of the Davis Nonet was the use of paired instrumentation. An example of this can be heard on the John Lewis arrangement "Move". In "Move", Lewis gives the melody to the pairing of trumpet and alto saxophone, baritone saxophone and tuba supply counterpoint, and trombone and French horn provide harmonies. Gerry Mulligan's "Jeru" demonstrates another Nonet hallmark: the use of a unison sound and rich harmony throughout the horns. Davis said, "I wanted the instruments to sound like human voices singing . . . and they did." Though the album is seen as a departure from traditional bop, the recordings do feature tunes that are considered close to the bop style, such as "Budo" which has the band bookending solos by Davis, Mulligan, Konitz, and Winding, similar to a bebop head arrangement.
One of the largest stated influences on the sound of The Birth of the Cool was band leader Claude Thornhill and his orchestra. Out of Thornhill's band came Lee Konitz, Gerry Mulligan, and Gil Evans, Miles Davis calling the Konitz-Mulligan-Evans incarnation "the greatest band" only after "the Billy Eckstine band with the Bird." The Thornhill band was known for its impressionistic style, innovative use of instrumentation, such as the use of tuba and French horn, and a no-vibrato playing style, hallmarks that the Miles Davis Nonet adopted for The Birth of the Cool. According to Evans:
“Miles had liked some of what Gerry and I had written for Claude. The instrumentation for the Miles session was caused by the fact that this was the smallest number of instruments that could get the sound and still express all the harmonies the Thornhill band used. Miles wanted to his idiom with that kind of sound.”
Davis saw the full 18-piece Thornhill orchestra as cumbersome and thus decided to split the group in half for his desired sound. As arrangers, both Evans and Mulligan give Thornhill credit for crafting their sound. Thornhill's band gave Evans the opportunity to try his hand at arranging small-group bebop tunes for big band, a practice few others were participating in. Mulligan recalls Thornhill teaching him "the greatest lesson in dynamics, the art of under blowing." Thornhill has also been credited with launching the move away from call and response between sections and the move towards unison harmonies.
The tracks from the January 1949 session were released soon after recording as two pairs of singles. From the April 1949 date, "Israel" and "Boplicity" were doubled together on a 78 and released as well. Of the twelve tracks recorded, Capitol released relatively few. In 1954, after persuasion from Rugolo, Capitol released eight of the tracks on a 10" record titled Classics in Jazz—Miles Davis. In 1957 eleven of the tracks (all except for "Darn That Dream") were released by Capitol as Birth of the Cool. The final track, "Darn That Dream" (the only song with vocals, by Hagood), was included with the other eleven on a 1971 LP. Subsequent releases have been based on this last arrangement. The album has since been reissued many times in various formats. The recordings of the nonet from its time at the Royal Roost were released as Cool Boppin. In 1998, Blue Note Records released The Complete Birth of the Cool, which was remastered by engineer Rudy Van Gelder and collected the nonet's live and studio tracks onto a single CD.
The band's original debut at the Royal Roost was positive but reserved reactions. Count Basie, the Roost's headliner during the Nonet's brief tenure, however, was more open to the groups sound, saying, "Those slow things sounded strange and good. I didn't always know what they were doing, but I listened, and I liked it."Winthrop Sargeant, classical music critic at The New Yorker, compared the band's sound to the work of an "impressionist composer with a great sense of aural poetry and a very fastidious feeling for tone color. . . The music sounds more like that of a new Maurice Ravel than it does like jazz . . . it is not really jazz."Though he did not recognize the record as jazz, Sargeant acknowledged that he found the record "charming and exciting".In the short term the reaction to the band was little to none, but in the long term the albums effects have been great and lasting. The album has been credited with starting the cool jazz movement as well as creating a new and viable alternative to bebop In 1957, after the release of the full Birth of the Cool, Down Beat magazine wrote that Birth of the Cool "[influenced] deeply one important direction of modern chamber jazz." Several tunes from the album, such as Carisi's "Israel", have gone on to become jazz standards.
Many members of the Miles Davis’ nonet went on to have successful careers in cool jazz, notably Gerry Mulligan and John Lewis. Mulligan moved to California and joined forces with trumpeter Chet Baker in a piano-less quartet, before creating his Concert Jazz Band Lewis would become music director of the Modern Jazz Quartet, which would become one of the most influential cool jazz groups. Evans would go on to collaborate with Davis again on the Davis albums Miles Ahead and Sketches of Spain. Following Birth of the Cool, Miles Davis did not return to cool jazz, instead going to play hard bop, and eventually spearheading modal jazz.