In 1967, Jacobs left the trio to study at the Juilliard School, and the Carpenter siblings were keen to try out other musical styles. Along with other musicians, including Gary Sims and John Bettis, the siblings formed the group Spectrum, which focused on a harmonious vocal sound and recorded many demo tapes in Osborn's garage studio, working out how to overdub voices onto multitrack tape. Many of those tapes were rejected by record companies. The group had difficulty attracting a live following, as their sound was too dissimilar from the hard rock and psychedelic rock then popular in clubs.