Drummer Buddy Miles was a groove maestro. But it’s his underrated songwriting and singing that steal the show here. One can’t escape the should-be-classic “Them Changes,” the stinging horns of the Jimi Hendrix–produced “69 Freedom Special,” or “Joe Tex,” a reverb-drenched instrumental salute to the Texas soul stirrer (and a rewrite of the Tex original “You’re Right, Ray Charles”). Dig the funk-freaky version of Gregg Allman’s “Midnight Rider” and the beautiful vocal harmonies on the smoldering live version of Neil Young’s “Down by the River.” This essential set was culled from the half-dozen worthy albums Miles did for Mercury Records from 1968 to 1971.