Bluegrass has a long tradition of a cappella singing, especially spirituals, and also onstage humor (usually between songs). “Atheists Don’t Have No Songs” combines all of that in a dead-on affectionate homage to bluegrass gospel, as put together by “World of Bluegrass” headliner with the host of the IBMA awards show, Brevard’s Steep Canyon Rangers. Here is a version from “Late Show With David Letterman,” with Martin’s solo vocal at the end bringing down the house as always. And that concludes our “Bluegrass for Beginners” series -- hope you liked it!