Ernie’s Record Mart was where many of Nashboro’s singles were sold. (Courtesy of Tompkins Square Label/Courtesy of Tompkins Square Label)

Nashville has for decades been known as the country music capital of the world, but that wasn’t the case before and immediately after World War II. Yes, the Grand Ole Opry had by then emerged as the nation’s premier radio barn dance. But in the years leading up to the birth of rock-and-roll, the town that became synonymous with country music was also home to a vibrant, diverse recording scene in which blues, pop, R&B and gospel contended with “hillbilly” music for popularity. Dominated not by major labels such as RCA and Columbia but by scrappy independents with evocative names like Bullet and Excello, Nashville’s music business was run by resourceful mavericks who cut deals — and hit records — in makeshift studios and storefronts.

Nashboro, the parent company of blues-based Excello, was one of the era’s most prolific purveyors of black gospel music, as witnessed, in this season of box-set riches, by Tompkins Square’s four-disc compendium, “I Heard the Angels Singing: Electrifying Black Gospel from the Nashboro Label, 1951-1983.” Many of the genre’s leading lights from the postwar period are featured among the collection’s 80 tracks, from the Chosen Gospel Singers and the Fairfield Four to Brother Joe May and Dorothy Love Coates and the Original Gospel Harmonettes. According to the liner notes of gospel authority Opal Louis Nations, the label’s only real competition at the time was from other indies such as Peacock and Savoy.

The brainchild of jukebox supplier Ernest L. Young, Nashboro was established mainly to stock the racks of Ernie’s Record Mart, the retail outlet through which Young furnished area jukes with product. Capitalizing on the wealth of local, regional and national talent that performed on radio and as part of the touring revues that often passed through Nashville, Young began hosting impromptu recording sessions in the back room of his store. Reaping a brisk return on his investment, he eventually built a proper studio on the third floor of his shop and founded Nashboro — and later, Excello, home to blues singers Slim Harpo and Lazy Lester — in 1951.

In effect, if not by design, Tompkins Square’s exemplary four-CD set plots the trajectory of Southern vernacular music in the mid-20th century. On the first CD, which spans 1951 to 1957, rockabilly rhythms mingle with barrelhouse piano and postwar jump blues, while on disc two, which covers 1958 to 1963, we hear R&B morphing into the harder-edged soul music patented by James Brown and Sam Cooke. “It’s Hard to Get Along,” a 1955 recording by the Swanee Quintet (who at one point toured with Brown) anticipates not just the Godfather’s 1956 R&B smash “Please Please Please,” but also the raspy soul of Cooke’s epochal 1963 recording from Miami’s Harlem Square Club.

The arrangements here tend to be loose and improvisational, everything from a cappella hand-clapping, shouting and foot-stomping to tremolo blues guitar to brushed snare drums backing close harmony singing redolent of doo-wop groups such as the Dominoes and the Drifters. Newcomers to this material will be struck by just how intimate the kinship was between sanctified and secular music of the period. Indeed, much of what is here bears witness to the proverbial, if by now cliched, adage about the gossamer-thin line between the earthy revelry of Saturday night and the celestial glories of Sunday morning.

Discs one and two are gleaming repositories of soul-stirring music from the golden age of black gospel quartet singing. (“Quartet,” incidentally, refers to the number of discrete voices in a group’s harmonic blend, not to how many singers make up a particular ensemble’s membership.) Nashville’s Skylarks, an offshoot of the by-then-disbanded Fairfield Four, are heard on two tracks on the first disc. “Baptism of Jesus,” the second of these, features the late Isaac “Dickie” Freeman, a basso profundo whose emoting and range rivaled that of the great Jimmy Ricks, the bass singer for the celebrated pop vocal group the Ravens.

Replete with swampy blues guitar, Miami’s Consolers offer a gutbucket rendering of “This May Be the Last Time,” the gospel standard typically credited to the Staple Singers that later became grist for the Rolling Stones’s 1965 pop hit, “The Last Time.” Milwaukee’s Supreme Angels, meanwhile, are heard on a pew-rocking version of the classic “Run to the Rock” and the Sons of Faith prefigure the throat-shredding groaning of Wilson Pickett with their unhinged take on “Since I’ve Been Born.” “Let the Church Roll On,” a 1960 recording by Sister Lucille Barbee, a.k.a “Nashville’s Queen of Gospel,” sports a rocking mambo beat akin to Bo Diddley’s signature hits from the era.

Covering 1964 to 1983, discs three and four find Nashboro settling into a steady and largely satisfying groove, its artists at times gravitating toward a more streamlined, pop sound (and often employing organ in favor of piano). In other instances, such as the Skylarks’s 1965 recording of “My Life Is in His Hands,” the progression is toward a heavier, more insistent soul reminiscent of Stax Records mainstays Johnnie Taylor and Sam and Dave. Sister Emma Tucker’s “You Should Have Been There” is another highlight, updating Sister Rosetta Tharpe’s rollicking proto-rockabilly gospel for the age of rock-and-roll. Elsewhere, stinging barbs of electric guitar echo the not-so-sanctified sounds of Mississippi’s Hill Country blues.

Voices better known in the realms of pop, soul and disco, such as those of Lou Rawls, Otis Clay and Candi Staton — artists who certainly were better known for the work they did for major record labels — can be heard throughout this collection. And yet “I Hear the Angels Singing” is more than just an opportunity to discover enthralling music known largely only to aficionados of deep, Southern-style gospel. Tompkins Square’s achievement also serves as a crucial reminder of how individuality can flourish — implicitly casting judgment on the corporatization of popular culture — in an unfettered climate like the one enjoyed by independent labels and artists in Nashville during the years immediately following the Second World War.

Friskics-Warren is a freelance writer.