Bluegrass royalty Leigh and Eric Gibson step into what some might at first see as uncharted territory on their country-soul breakout Mockingbird, the latest album. The celebrated bluegrass duo — named back-to-back Entertainers of the Year by the International Bluegrass Music Association in 2012 and 2013 — played the Nashville game two decades ago, while in their early 20s, and were offered a major label deal, only to be told at the last minute that they were too “retro” for modern country music. Today, such characterizations, along with their authenticity, set them apart. A mix of country, soul and seventies rock, the sibling duo are musical trailblazers. As players and vocalists, they are superb, harmonizing as only siblings can; as songwriters they stand without peer, having long been a band awarded for their songs and songwriting.