Founded in 1971 by local R & B writer-producers Kenny Gamble and Leon Huff, Philadelphia International Records was designed to be a hit factory — a Motown with East Coast swagger, a Stax with silken swing — and this four-CD history tells the tale as they intended. Opening with a smash — the Soul Survivors' "Expressway (To Your Heart)," a 1967 blast of psychedelic funk from Gamble and Huff's freelance years — Love Train keeps on giving with dozens of top R&B and pop singles, many by the O'Jays ("Backstabbers" and the set's title song), Harold Melvin and the Blue Notes ("The Love I Lost," "Wake Up Everybody"), Philly honeys the Three Degrees ("When Will I See You Again") and the Intruders ("I'll Always Love My Mama"). Everything is familiar magnificence, including the polished grit Gamble and Huff first produced for other labels (Jerry Butler's "Only the Strong Survive," Dusty Springfield's "Brand New Me") and later outside jobs for the Manhattans and the Jacksons.

Ironically, the commercial peak of the sustained apex across Discs Two and Three is an instrumental: "T.S.O.P. (The Sound of Philadelphia)," the 1974 Number One single by the PIR studio orchestra, MFSB. What you hear everywhere else is a singer's paradise. The star voices — the Blue Notes' Teddy Pendergrass, the O'Jays' Eddie Levert, the Spinners' Philippe Wynn — are perfectly cushioned but never crowded by the penthouse-party sparkle. When Pendergrass rages in his black-lion's roar about the high price of daily ghetto life in 1975's "Bad Luck," the streets of Philadelphia cut through those strings, loud and clear.