Composer Thomas A. Dorsey and other pioneers of gospel music helped open the church doors to music considered sinful by conservative churchgoers. In the 1930s, Dorsey livened up the hymnal by incorporating elements of blues and jazz. Early "Sanctified" churches also influenced the restrained environment of mainline churches. Sanctified preachers encouraged the congregation to spontaneously burst into improvised musical lines to express their faith. Following in the footsteps of this stylistic freedom, groups such as the Golden Gate Quartet and the Five Blind Boys of Mississippi began ad-libbing in their jubilee style of gospel music. Jubilee is characterized by a strong, pumping bass, and lead vocals that ride the line between spoken and sung. The Golden Gate Quartet and other four-part choral groups showcased stunning solos and intricate harmonies. The tradition of gospel quartets continues to lift the spirits of both its listeners and participants in concert halls and churches alike.