Jazz-funk is a sub genre of jazz music characterized by a strong back beat, electrified sounds and an early prevalence of analog synthesizers. The integration of funk, soul, and R&B music and styles into jazz resulted in the creation of a genre whose spectrum is quite wide and ranges from strong jazz improvisation to soul, funk or disco with jazz arrangements, jazz riffs, and jazz solos, and sometimes soul vocals. Jazz-funk is primarily an American genre, where it was popular throughout the 1970s and the early 1980s, but it also achieved noted appeal on the club-circuit in England during the mid-1970s. Similar genres include soul jazz and jazz fusion, but neither entirely overlap with jazz-funk. Notably jazz-funk is less vocal, more arranged and featured more improvisation than soul jazz, and retains a strong feel of groove and R&B versus some of the jazz fusion production.