Jazz bass is the use of the double bass or bass guitar to improvise accompaniment ("comping") basslines and solos in a jazz or jazz fusion style. Players began using the double bass in jazz in the 1890s to supply the low-pitched walking basslines that outlined the chord progressions of the songs. From the 1920s and 1930s Swing and big band era, through 1940s Bebop and 1950s Hard Bop, to the 1960s-era "free jazz" movement, the resonant, woody sound of the double bass anchored everything from small jazz combos to large jazz big bands.