Among alternative tunings for guitar, each **augmented-fourths tuning** is a regular tuning in which the musical intervals between successive open-string notes are each *augmented fourths*. Because augmented fourths are alternatively called "tritones" ("tri-tones") or "diminished fifths", augmented-fourths tuning is also called **tritone tuning** or **diminished-fifths tuning**.

The standard guitar-tuning

E-A-d-g-b'-e'

interjects exactly one major third amid four perfect fourths for the intervals between its successive open strings. In contrast, the augmented fourths tunings

C-F

♯-c-f

♯-c'-f '

♯ and
B-F-b-f-b'-f'

have only augmented-fourths intervals.

The set of augmented-fourths tunings has three properties that simplify learning by beginners and improvisation by experts: Regular intervals, string repetition, and lefty-righty symmetry. These properties characterize augmented-fourths tunings among non-trivial tunings.

The set of augmented-fourths tunings has three properties that simplify learning by beginners and improvisation by experts: Regular intervals, string repetition, and lefty-righty symmetry.

Besides the set of augmented-fourths tuning, exactly one other set of tunings has these three properties—the *trivial* class of one-note tunings, which contains the C-C-C-C-C-C tuning, for example.

Augmented-fourths tunings have extended range. Because each of its tritone-intervals between successive strings is wider than the perfect-fourth intervals (and one major third) of standard tuning, augmented-fourths tunings have greater range than standard tuning—six additional notes, only one less note than Robert Fripp's new standard tuning.

In each *regular tuning*, the musical intervals are the same for each pair of consecutive strings. Other regular tunings include major-thirds, all-fourths, and all-fifths tunings. For each regular tuning, chord patterns may be moved around the fretboard, a property that simplifies beginners' learning of chords and that simplifies advanced players' improvisation.

Two other regular tunings, all-fourths and all-fifths tunings, have strings with five and six distinct open-notes, respectively. Thus, they have no repetition of open-notes, and so they require that the guitarist remember five and six strings, respectively.

In contrast, augmented fourths is a repetitive tuning that begins the next octave after two strings. These tunings' repetition of open-string notes again simplifies the learning of chords and improvisation.

For left-handed guitars, the ordering of the strings reverse the ordering of right-handed guitars. Consequently, left-handed tunings have different chords than right-handed tunings. Regular guitar-tunings have the property that their left-handed ("lefty" versions) are also regular tunings. For example, the left-handed version of all-fourths tuning is all-fifths tuning, and the left-handed version of all-fifths tuning is all-fourths tuning. In general, the left-handed involute of the regular tuning based on the interval with
n
semitones is the regular tuning based on its involuted interval with
12
−
n
semitones: All-fourths tuning is based on the perfect fourth (five semitones), and all-fifths tuning is based on the perfect fifth (seven semitones), as mentioned previously.

The left-handed involute of an augmented-fourth tuning is the augmented-fourths tuning with the same open-string notes. "The augmented-fourth interval is the only interval whose inverse is the same as itself. The augmented-fourths tuning is the only tuning (other than the 'trivial' tuning C-C-C-C-C-C) for which all chords-forms remain unchanged when the strings are reversed. Thus the augmented-fourths tuning is its own 'lefty' tuning."

The "standard tuning" consists of perfect fourths and a single major-third between the G (g) and B (b') strings:

E-A-d-g-b'-e'

Of all the augmented-fourths tunings, the C-F♯-c-f♯-c'-f '♯ tuning is the closest approximation to the standard tuning, and its fretboard is displayed next:

Each fret displays the open strings of exactly one augmented-fourths tuning.

There are no sharps in the open strings of exactly one augmented-fourths tuning, that with only B and F notes (B-F-b-f-b'-f'). This tuning would appear, for the C-F♯ augmented-fourths tuning displayed above, to the left of the open strings, at the *negative*-first fret.

This tuning "makes it very easy for playing half-whole scales, diminished 7 licks, and whole tone scales," stated guitarist Ron Jarzombek, who has used it on two albums. This tuning was used in "Tri 7/5" by Shawn Lane (*The Tri-Tone Fascination* and *Powers of Ten; Live!*).