Some piezo-equipped guitars use a hexaphonic pickup. "Hex" is a prefix meaning six. A hexaphonic pickup produces a separate output for each string, usually from a discrete piezoelectric or magnetic pickup for each string. This arrangement lets on-board or external electronics process the strings individually for modeling or Musical Instrument Digital Interface (MIDI) conversion. Roland makes hexaphonic pickups for guitar and bass, and a line of guitar modeling and synthesis products. Line 6's hexaphonic-equipped Variax guitars use on-board electronics to model the sound after various vintage instruments, and vary pitch on individual strings.
Adjusting the truss rod affects the intonation of a guitar as well as the height of the strings from the fingerboard, called the action. Some truss rod systems, called double action truss systems, tighten both ways, pushing the neck both forward and backward (standard truss rods can only release to a point beyond which the neck is no longer compressed and pulled backward). The artist and luthier Irving Sloane pointed out, in his book Steel-String Guitar Construction, that truss rods are intended primarily to remedy concave bowing of the neck, but cannot correct a neck with "back bow" or one that has become twisted.[page needed] Classical guitars do not require truss rods, as their nylon strings exert a lower tensile force with lesser potential to cause structural problems. However, their necks are often reinforced with a strip of harder wood, such as an ebony strip that runs down the back of a cedar neck. There is no tension adjustment on this form of reinforcement.
SFCM produces some of the most successful and influential classical guitarists in the world. Spearheaded by renowned faculty and complemented by visiting artists such as Marcin Dylla, the department honors the tradition of the classical guitar while cultivating innovation. The Harris Guitar Collection, housed at SFCM, gives students a chance to see—and play—some of the most extraordinary guitars of the last two centuries.