AllMusic Guide states that "until around 1967, the worlds of jazz and rock were nearly completely separate". The term, "jazz-rock" (or "jazz/rock") is often used as a synonym for the term "jazz fusion". However, some make a distinction between the two terms. The Free Spirits have sometimes been cited as the earliest jazz-rock band. During the late 1960s, at the same time that jazz musicians were experimenting with rock rhythms and electric instruments, rock groups such as Cream and the Grateful Dead were "beginning to incorporate elements of jazz into their music" by "experimenting with extended free-form improvisation". Other "groups such as Blood, Sweat & Tears directly borrowed harmonic, melodic, rhythmic and instrumentational elements from the jazz tradition". The rock groups that drew on jazz ideas (like Soft Machine, Colosseum, Caravan, Nucleus, Chicago, Spirit and Frank Zappa) turned the blend of the two styles with electric instruments. Since rock often emphasized directness and simplicity over virtuosity, jazz-rock generally grew out of the most artistically ambitious rock subgenres of the late 1960s and early 70s: psychedelia, progressive rock, and the singer-songwriter movement. Miles Davis' "Bitches Brew" sessions, recorded in August 1969 and released the following year, mostly abandoned jazz's usual swing beat in favor of a rock-style backbeat anchored by electric bass grooves. The recording "...mixed free jazz blowing by a large ensemble with electronic keyboards and guitar, plus a dense mix of percussion." Davis also drew on the rock influence by playing his trumpet through electronic effects and pedals. While the album gave Davis a gold record, the use of electric instruments and rock beats created a great deal of consternation amongst some more conservative jazz critics.