Bluegrass is a genre of music that utilizes acoustic instruments such as the banjo, fiddle, mandolin, upright bass and dobro. It is characterized by a high-pitched sound with tight harmonies as band members often gather around the same microphone to sing. It is also often performed by brother duets such as Bill and Charlie Monroe and Ralph and Carter Stanley. Bluegrass was founded by Bill Monroe and was later made popular by festivals, the Grand Ole Opry and movies such as O Brother, Where Art Thou? and Deliverance. It has influences from other genres of music such as old-time, folk, jazz, blues and gospel. Themes of bluegrass center around simple country life, religion, family, hard work and tradition. Bluegrass musicians have made changes to stay competitive in the music industry throughout the years, such as occasionally incorporating electric instruments into their work. However, bluegrass still remains true to its roots and continues to be a popular and growing music genre today.