Simply to speak the city's name evokes a sharp sense of loss, but in truth Louis Armstrong's New Orleans was long gone. Pete Lala's club, Joe Segretta's saloon, Funky Butt Hall – virtually all the landmarks of his youth had been obliterated by time or urban redevelopment years before Katrina. Part of the fascination of this book lies in Brothers's ability to restore that lost world of uptown and downtown, black and Creole, street cries and fish fries, the whole boiling primeval soup of ragtime, blues and jazz. The photographs are grainy, the ancient city maps crabbed, but Brothers writes in living colour, peopling the streets of early 20th century New Orleans with its hustlers, whores and horn-blowers. The story of a poor boy who became the jazz library's richest donor has been told many times, not least by the man himself, whose vivid letters and taped reminiscences Brothers edited in Louis Armstrong In His Own Words (1999). Most of Armstrong's biographers have belonged to the generation that acquainted itself with him through his recordings in Chicago in the 1920s, first with his mentor King Oliver, then leading studio bands such as the Hot Five and Hot Seven. The central motif of their accounts is the creative fire that Louis stoked in those years, the flaming imagination of performances like 'Potato Head Blues'. A second theme, very often, is the artistic diminuendo of his later career, the swoop (as they see it, though Armstrong would not) from 'Struttin' With Some Barbecue' to 'Hello, Dolly' and 'What A Wonderful World'.

Brothers, however, finds a new story to tell – by the ingenious ploy of stopping just as the familiar story begins. It is not until page 272 that he sees Armstrong on to the train for Chicago, and barely 30 pages later the narrative (apart from the considerable endmatter) is over. You might say it is an account of Armstrong before anything happened to him, but Brothers's point is that these teenage years of hustling and musical self-education in the Odd Fellows Hall or at the pier-parties of Lake Pontchartrain were when everything happened to him, every musical memory stored, every life-lesson ingrained.

When he recorded 'Potato Head Blues' in 1927, as he recalled years afterwards, he was picturing the friends of his youth like Joe Oliver and trombonist Kid Ory, and the dancehall where they used to play on Rampart and Gravier Streets: "Every note that I played on this recording, I thought of Papa Joe." Louis could never have known what it means to miss New Orleans, for he took it with him everywhere he went.

There have been attempts in recent years to question the established narrative of early jazz and destabilise the position of New Orleans as its founding city. Although too polite a scholar to elbow aside a contrary view, Brothers clearly feels that in this matter the received opinion is the right one, and indeed his book does much to advance the case by showing that no other American city provided so fertile a matrix for the culturally heteregeneous music that came to be called jazz – though not, at the time, by the musicians who played it. Crucially, it was only New Orleans that witnessed the confluence of two streams without which jazz as we know it would have been inconceivable: the schooled, Europeanised music of the downtown Creole players, who valued good tone and accurate reading, and the autodidacticism of the uptown African-Americans, who compensated for musical illiteracy by developing the arts of melodic variation ('ragging the tune'), collective improvisation and, what was especially attractive to the young Armstrong, weaving endlessly varied patterns with the three-ply harmony of the blues.

Brothers is excellent on the musicology – he is surely the only jazz scholar who has also written on chromaticism in the late mediaeval chanson – but he is equally skilful in his detailing of the social structures in and around which the music was made. A network of fraternal organisations, of lodges and 'pleasure clubs' like the Zulus, the Jolly Boys and the Diamond Swells, enabled boys to become apprenticed to the craft of music and men to earn status for it.

The primary expressive outlet for these societies was the funeral: "Though manly dignity was under daily attack in life – because it was under attack – it could be ensured at the moment of death via club membership and a grand, public display.… The beginning of the African-American embrace of this ritual… coincided with the beginnings of harsh post-Reconstruction retrenchment from political rights, and the practice ended – not totally, but as an organic demonstration of civic life – when civil rights came to fruition, as if to make clear the political nature of the ritual." Expanded and enriched by such insights, Louis Armstrong's New Orleans is an account of much more than the man or the city: penetrating the shadowy alleys of the past, it illuminates the heroic self-emancipation of expressive culture in black America.