Think of this as the Grateful Dead “Unplugged.” Years before MTV started its popular series of intimate concerts, the Dead culled together two double-albums’ worth of acoustic material from their 23-show run at the Warfield Theater in San Francisco and Radio City Music Hall in New York, in September and October of 1980. Coming from a bluegrass background, this is an entirely natural setting for the Dead, but what’s really remarkable is that these performances offer revelations even as they affirm the essence of the band’s art. Taking away the electricity gives the songs a new texture and sense of space. There has never been a rock band able to play as gently as the Dead, but these versions of “Oh Babe It Ain’t No Lie,” “China Doll,” and “To Lay Me Down” elevate the band to new plateaus of warmth and delicacy. Immaculately recorded and impeccably performed, Reckoning nonetheless retains the air of an impromptu picking session. This might just be the most elegant, poignant bluegrass outfit you’ll ever hear.