Jazz-funk is a sub-genre of jazz music characterized by a strong back beat (groove), electrified sounds, and often, the presence of the first electronic 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 indeed 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 improv than soul jazz, and retains a strong feel of groove and R&B versus some of the jazz fusion production.