Lesh was an innovator in the new role that the electric bass developed during the mid-1960s. Contemporaries such as Casady, Bruce, James Jamerson and Paul McCartney adopted a more melodic, contrapuntal approach to the instrument; before this, bass players in rock had generally played a conventional timekeeping role within the beat of the song, and within (or underpinning) the song's harmonic or chord structure. While not abandoning these aspects, Lesh took his own improvised excursions during a song or instrumental. This was a characteristic aspect of the so-called San Francisco Sound in the new rock music. In many Dead jams, Lesh's bass is, in essence, as much a lead instrument as Garcia's guitar.