One of the unremarked aspects of the current ’70s soul revival is that many of its practitioners haven’t paid their dues. Alicia Keys was barely out of high school before she got a recording contract, and Maxwell spent more time in the penthouse listening to Marvin than he did at the club imitating him. Frank McComb, though, was 21 when he started working with the Rude Boys in 1991, and has since done vocal and keyboard work for jazz taskmaster Wynton Marsalis and the Gamble-Huff production team. His first solo album, released in 2000, sank from sight because Sony didn’t know if it should be marketed as smooth soul or jazz. His second, independently recorded album, “The Truth Volume One,” is a clearer demonstration of purpose. Steeped in the funky, keyboard-propelled R&B of early ’70s Stevie Wonder and sounding like a lighter Donny Hathaway, McComb emphasizes originality over drama and tight arrangements over showing off his skills, which are nevertheless impressive when he deigns to show them off. Restraint is often more thrilling than abandon.