If imitation is truly the sincerest form of flattery, then the classic Philly soul sound of the early to mid-'70s must have occupied the most overtly flattered wing in all of the American R&B canon. Over the years, that sweeping, romantic, hook-filled, string-laden sound has been aped by everyone from Hall & Oates to Difford & Tillbrook to Lenny Kravitz, with varying degrees of success. The four-disc Love Train box goes a long way toward explaining the Philly soul obsession that's continued to exist ever since the heyday of the Spinners, the O'Jays and Teddy Pendergrass.

The empire that producers/songwriters Kenny Gamble and Leon Huff built around the artists on their Philadelphia International label in the '70s is given a definitive and loving document with these four discs, not to mention a handsome, elaborate booklet, packed with photos, detailed info and thoughtful essays and interviews. Things move along chronologically, beginning with the late-'60s hits Gamble and Huff masterminded before establishing Philly International, like the Delfonics' "La-La Means I Love You," and the Intruders' "Cowboys to Girls" before moving into genre-defining early-'70s PI singles like the O'Jays' socially conscious "Back Stabbers" and Billy Paul's nice 'n' naughty "Me and Mrs. Jones." With tart but lush string arrangements, percolating grooves and emotive pop-soul vocal performances, these tracks were the sound of pop radio in the '70s.

Moving along a few years further into the decade, with the Gamble/Huff army still marching along at full power, the seeds of disco can be heard in 1975 hits like Harold Melvin & the Blue Notes' "Bad Luck" and the O'Jays' "I Love Music." And sure enough, these were just the kind of records that the earliest disco DJs were spinning at those pre-Studio 54 goodfoot gatherings. Later cuts such as McFadden & Whitehead's propulsive anthem of optimism "Ain't No Stoppin' Us Now" and Teddy Pendergrass's much-covered "Love T.K.O." found the label pushing into a new decade, at the vanguard of a new era of pop/R&B crossovers.

In subsequent years, everyone from Brit-soulsters Simply Red to former Doobie Brother Michael McDonald would have hits with their own versions of some of the songs on Love Train, and while the continued commercial viability of these tunes can't help but speak to their staying power, in the words of a song that emerged from that other classic R&B/pop crossover empire, "ain't nothing like the real thing." And that's what you get with this top-shelf set.