There have been six installments in the I Heard It on NPR series to date, three of which -- "Down to the Roots," "Singers, Songs & Sessions," and "One World Many Voices" -- are included in this box set. There are several gems on each of these albums, but what you have here is in effect an extended sampler, and the safe, quaint tone that dominates (and practically defines NPR) gets a little irritating after a while, and one starts to long for a couple of Sex Pistols tracks just to clear out the ears. "Down to the Roots" focuses on bluegrass, gospel, and country artists, and the clear highlights are the first two tracks, Ollabelle's call-and-response gospel stomper, "Before This Time," followed by the equally as passionate (and every bit as upbeat) "It Just Suits Me," which pairs American treasures Hobart Smith and Bessie Jones. Another pairing here is even odder (but no less successful), with Norah Jones joining Dolly Parton for "Creepin' In," a wonderful bit of Appalachian pop full of mountain harmonies. "Singers, Songs & Sessions" is a collection of live-in-the-studio performances from several singer/songwriter types, and it is veteran Randy Newman who steals the show with a stripped-down rendition of his beautiful and tragic farce "Sail Away." "One World Many Voices" focuses on mostly international tracks in what is a clear attempt to show how interlinked the planet's music actually is. The selections range from the soulful folk of the late Eva Cassidy to the classic reggae spiritual "Rivers of Babylon" by the Melodians. If there's a problem with this NPR series, it's that nothing is ever too jarring, and while there is no denying that one of music's many purposes is to soothe, it also needs to -- at times, anyway -- rattle and roll and occasionally even piss people off. None of that is here.