Discover your guitar's true voice. MTR13 Retro Bluegrass (Tony Rice's Choice) acoustic guitar strings are the real deal, not an imitation. With Martin MTR13 Retros, you get one tough set of strings that will last a long time and give you true, consistent tone that sounds like nothing else on the market. Martin's proprietary SOLID nickel/copper alloy blend provides for a reduced pick attack which allows the guitar's tone woods to be heard, not overshadowed. It offers uniquely mellow, yet crisp, sound. Martin's proprietary wrap wire is naturally corrosion resistant.