Acoustic bass guitar of acoustic bass guitars. The bajo sexto, with six pairs of strings, resembles a twelve-string guitar tuned an octave lower. The heavy gauge strings generate a large string tension, yet the guitar is built relatively lightly. Musicians began to use the bajo sexto in Texas in the 1920s with the rise of "Tex-Mex" music, and remains in common use to play parts that would be played by the piano in traditional American popular music. It matches the standard tuning of a 12-string guitar, one octave lower. The tuning of these instruments is (capital letters are an octave lower than small
Twelve-string guitar an octave lower) to achieve a very rich, complex sound. The greater number of strings offers almost endless possibilities. Nashville Tuning refers to a way of simulating a 12-string guitar sound, using two six-string guitars playing in unison. This is achieved by replacing the lower four courses on one six-string with the higher octave strings for those four courses from a 12-string set, and tuning these four strings an octave higher than normal tuning for those courses on a six-string. Double-tracking this guitar with the standard-tuned six-string is commonly used in recording studios to achieve a "cleaner" 12-string effect. The