others only use guide marks on the side of the neck. Tapewound (double bass type) and flatwound strings are sometimes used with the fretless bass so that the metal string windings do not wear down the fingerboard. Some fretless basses have epoxy-coated fingerboards to increase durability, enhance sustain, and give a brighter tone. Though most fretless basses have four strings, five-string and six-string fretless basses are also available. Fretless basses with more than six strings are also available as "boutique" or custom-made instruments. Alternative instruments While the majority of jazz and jazz fusion recordings and live performances use either the double bass (or a related instrument such as an electric upright bass) or the electric bass to supply the "low end", there are some exceptions. In jazz organ trios, a Hammond organ player performs the basslines using the bass pedalboard or their lower manual, along with a drummer and a saxophonist. In some jazz fusion groups, the basslines may be played by a keyboard player on a bass synthesizer or other keyboard. As well, in some duos and other small groups, the basslines may be provided by a piano player; in a duo consisting of a jazz pianist and a jazz singer, the piano player plays a bassline with the left hand and chords in the right hand underneath the singer's voice. Similarly, in some duos or trios, a jazz guitarist may play basslines, a role that is especially feasible if the guitarist has a seven-string guitar with a low "B" string. In traditional Dixieland or New Orleans-style jazz groups, the basslines may be played by a tuba or other low brass instrument. See also Swing (jazz performance style) List of bassists List of jazz bassists References Further reading Forward Motion by Hal Galper: An approach to Jazz Phrasing. Jazz instruments Amplified instruments Double basses Bass guitars Accompaniment Occupations in music Bass (sound) Jazz fusion Rhythm section