Drawn from the folk boom of the ’60s, this robust collection of protest music evokes a bygone era, but the message of the music has retained (or perhaps regained) its urgency. The performers draw on a rich heritage witnessed by Jack Elliott’s engaging version of Woody Guthrie’s “1913 Massacre” and Odetta’s haunting take on “No More Auction Block for Me.” Dylan scholars will note his duet with Pete Seeger on the obscure “Playboys and Playgirls.” But Let Freedom Sing isn’t just a history lesson: The anti-war sentiments of Phil Ochs’ classic “I Ain’t Marchin’ Anymore” are as compelling and pertinent as ever.