Kevin Salem, with Carolyn's Mother, Tuesday, April 4, at Herman's Hideaway, is the sort of performer who gets overlooked by everyone other than reviewers--and they overlook him most of the time, too. That's a pity, because Salem (onetime member of Boston's late, occasionally lamented Dumptruck and sideman for, among others, Freedy Johnston, Miracle Legion and Yo La Tengo) is that rare performer whose songs mean more simply because he delivers them so passionately. Soma City, his debut for the Roadrunner label, sneaks up on you: The material sounds commonplace just long enough for you to be pleasantly surprised when his words and melodies won't leave you alone. And, as Salem proved during his showcase at this year's South By Southwest music conference, he's pretty damn good live, too. Not that anyone other than a few reviewers bothered to notice.