You'd think Virginia's Keller Williams would get lonely every once and a while, having spent almost two decades creating the ghostly illusion of a backing band through his signature Gibson Echoplex looping unit, delivering numerous albums' worth of material that adhere to the foundation of a good riff, and the complex compositions that can be constructed around its foundation. Incorporating splashes of bluegrass, jazz, funk, even reggae in his one-man, jam-band calling card, Williams has maintained the ability to be a showman without being a showoff. Featuring a blend of his solo work and material with friends Claude Arthur, Jay Starling and Toby Fairchild, Williams is scheduled to perform at the National on Wednesday, Dec. 20, at 7 p.m. $18-$21.