In its earliest incarnation during the mid-'60s, Jazz-Funk was an earthy amalgamation of jazz and funky Southern soul, also heavily influenced by the proto-funk innovations of Sly & the Family Stone. In that respect, it was fairly similar to soul-jazz, but where soul-jazz was often content to lay back in the groove, jazz-funk drove forward with a stronger, more pronounced backbeat, as well as a more explicit devotion to the Stax/Volt brand of soul music (sometimes reflected in cover versions of popular soul hits). Many early jazz-funk artists were organists, like Lonnie Smith, Reuben Wilson, Charles Earland, and Jack McDuff (some of whom crossed freely between jazz-funk and soul-jazz); other key figures included saxophonist Eddie Harris and vibraphonist Roy Ayers. As the grittier strain of soul metamorphosed into funk during the early '70s, and as fusion helped make funk rhythms a compelling way for some hard boppers to reconnect with their African-American audience, the crucial R&B component of jazz-funk shifted with the times. Artists like trumpeter Donald Byrd, flautist Bobbi Humphrey, and keyboardist Ronnie Foster crafted a sunny, breezy style by performing compositions which often simply resembled jazzy R&B, and drew from Philly soul as well as funk. Keyboardists like Herbie Hancock and Lonnie Liston Smith explored a spacier, more atmospheric brand of jazz-funk, while the artists on Creed Taylor's CTI label (most prominently Freddie Hubbard) were wrapped in a shinier, more polished production. Fusion and jazz-funk shared many sensibilities during the early '70s, but it's important to realize that not all fusion was jazz-funk, and vice versa. Fusion could encompass a greater variety of moods and influences, whereas jazz-funk was always marked by its devotion to R&B, and maintained the upbeat, celebratory vibe of funk. Just as funk was eventually smoothed out into disco, jazz-funk melted into the smoother, more polished brand of crossover-oriented fusion that dominated the popular, more accessible side of jazz during the '80s and '90s. Because of its emphasis on danceable, funky grooves, jazz-funk became highly popular in the British underground music scene (where it was known as "rare groove") when it was rediscovered during the mid- to late '80s; an update version mixed with funk and hip-hop became known as acid jazz. For similar reasons, jazz-funk was also the style to which many American hip-hop artists turned when looking for ways to fuse jazz and rap; Roy Ayers, in particular, enjoyed a renaissance and reappraisal in both scenes. Plus, artists like Medeski, Martin & Wood helped revive the classic jazz-funk sound and bring it to newer, wider audiences in the '90s.