Bluegrass music was pioneered by Bill Monroe and his band, the Blue Grass Boys. It is a subgenre of country music characterized by acoustic string instruments and 'high lonesome' vocal harmonies. A standard bluegrass ensemble includes the fiddle, five-string banjo, acoustic guitar, mandolin, and upright bass. Unlike mainstream country, bluegrass avoids electric instruments and drums, relying on the 'chop' of the mandolin and the driving roll of the banjo for rhythm. It emphasizes fast-paced, virtuosic soloing where each musician takes turns improvising over the melody, similar to jazz. The style is rooted in the traditional music of Appalachia, with strong influences from Scottish and Irish folk music.