A few weeks ago, music fans mourned the loss of Teddy Pendergrass, a paragon of refined, sensual soul music who was almost certainly the finest voice to come from the Philly soul scene. But Pendergrass was just one of the many stars nurtured by Kenny Gamble and Leon Huff's Philadelphia International Records. A reissue series of the label's deep archives brought this music back into the public consciousness, and now two of PIR's biggest acts, the O'Jays and Patti LaBelle, have paired up for a Valentine's Day concert. Best remembered for "Love Train," the O'Jays made a mark with other well-orchestrated hits such as "Use Ta Be My Girl" and the immortal "Back Stabbers." LaBelle found more enduring fame in the '80s with a sound that moved toward pop and adult-contemporary. Her duet with Michael McDonald on 1986's "On My Own" is an instance of distilled heartbreak.