A musician who has played sideman to such esteemed figures as Lyle Lovett and Emmylou Harris, Sam Bush is an innovative mandolin virtuoso, and that’s not to mention his skills as a fiddler, singer and songwriter. A native of Bowling Green, Ky., Bush turned 60 this year, and he’s been recognized by his home state as “Father of Newgrass,” among many other honors. Whatever your definition of Newgrass may be, Bush has certainly pushed the boundaries of Bill Monroe’s music. Bush’s discography is vast, as befits a man who appreciates both Jethro Burns and John McLaughlin, and I wouldn’t know where to tell you to start — maybe you could begin with his fine 2009 full-length, Circles Around Me. Talk about expanding subject matter: Along with Guy Clark and Verlon Thompson, Bush wrote the amazing “The Ballad of Stringbean and Estelle,” which is about murder and country music.