Williams needed only a three-piece backing band to make her point. Guitarist Stuart Mathis provided spare, excellently melodic contributions, but the focus was entirely on these songs. Williams never had a traditionally pretty voice, but her salty Louisiana drawl was all the more convincing for it Tuesday. Tales of rural malaise and rock-'n'-roll tragedies from her groundbreaking 1998 album “Car Wheels on a Gravel Road” sounded only more hard-won. “2 Cool to Be 4-gotten,” “Greenville” and “Drunken Angel” perfected that mix of romance, regret and self-inflicted wounds that the best country delivers.