Like Regina Belle, Howard is a new-generation R&B; singer who emerged in the mid-'80s. Both like to dabble with jazz, but each sounds best when opting for the unburnished soul route. Like Belle, Howard (who headlines the Roxy tonight and Monday) is a stylish vocalist who is frequently at the mercy of her producers and material. When they’re not in peak form, she can’t always rise above them. The producer who serves Howard best on this project is Nick Martinelli. The sure touch he supplies on “Love Under New Management” is superb and he gets a rich, gospel-fueled performance out of the Chicago-born singer. The rest of the album is spotty, going from excellent on the funky little exercise “Ain’t Nuthin’ in the World,” to lackluster on a version of Aretha Franklin’s “Until You Come Back,” a track that flounders because it’s too tame and faithful to the original.