An
augmented sixth is one of four musical intervals that span six
diatonic scaleIn music theory, a diatonic scale is a seven note musical scale comprising five whole steps and two half steps, in which the half steps are maximally separated...
degrees. The prefix 'augmented' identifies it as being the largest of the four intervals; the others being the
major sixthA major sixth is the larger of two commonly occurring musical intervals that span six diatonic scale degrees. The prefix 'major' identifies it as being the larger of the two ; its smaller counterpart being a minor sixth. The major 6th is abbreviated as M6, and its inversion is the minor third...
,
minor sixthA minor sixth is the smaller of two commonly occurring musical intervals that span six diatonic scale degrees. The prefix 'minor' identifies it as being the smaller of the two ; its larger counterpart being a major sixth...
, and diminished sixth, which are one, two, and three
semitoneA semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music, and it is considered the most dissonant. The most commonly written form of this interval is the minor second, notated using two adjacent letter names A semitone, also called a...
s smaller, respectively.
Its inversion is the
diminished third, and its
enharmonicIn modern music and notation, an enharmonic equivalent is a note , interval , or key signature which is equivalent to some other note, interval, or key signature, but "spelled", or named, differently...
equivalent is the
minor seventhA minor seventh is the smaller of two commonly occurring musical intervals that span seven diatonic scale degrees. The prefix 'minor' identifies it as being the smaller of the two , its larger counterpart being a major seventh. The minor seventh is abbreviated as m7 and its inversion is the major...
; In
septimal meantone temperamentIn music, septimal meantone temperament, also called standard septimal meantone or simply septimal meantone, refers to the tempering of 7-limit musical intervals by a meantone temperament tuning in the range from fifths flattened by the amount of fifths for 12 equal temperament to those as flat as...
, it is specifically equivalent to the
harmonic seventhThe harmonic seventh interval , also known as the septimal minor seventh, or subminor seventh, is one with an exact 7:4 ratio . This is somewhat narrower than and is "sweeter in quality" than an "ordinary" minor seventh, which has a just-intonation ratio of either 16:9 or 9:5, or an...
(a
just intervalIn music, just intonation is any musical tuning in which the frequencies of notes are related by ratios of whole numbers. Any interval tuned in this way is called a just interval; in other words, the two notes are members of the same harmonic series....
of 7/4).
In the tuning system known as
equal temperamentEqual temperament is a musical temperament, or a system of tuning in which every pair of adjacent notes has an identical frequency ratio. In equal temperament tunings, an interval — usually the octave — is divided into a series of equal steps...
the augmented sixth is equal to ten semitones and is a
dissonantIn music, a consonance is a harmony, chord, or interval considered stable, as opposed to a dissonance — considered unstable...
interval.
The augmented sixth is relatively rare.
An
augmented sixth is one of four musical intervals that span six
diatonic scaleIn music theory, a diatonic scale is a seven note musical scale comprising five whole steps and two half steps, in which the half steps are maximally separated...
degrees. The prefix 'augmented' identifies it as being the largest of the four intervals; the others being the
major sixthA major sixth is the larger of two commonly occurring musical intervals that span six diatonic scale degrees. The prefix 'major' identifies it as being the larger of the two ; its smaller counterpart being a minor sixth. The major 6th is abbreviated as M6, and its inversion is the minor third...
,
minor sixthA minor sixth is the smaller of two commonly occurring musical intervals that span six diatonic scale degrees. The prefix 'minor' identifies it as being the smaller of the two ; its larger counterpart being a major sixth...
, and diminished sixth, which are one, two, and three
semitoneA semitone, also called a half step or a half tone, is the smallest musical interval commonly used in Western tonal music, and it is considered the most dissonant. The most commonly written form of this interval is the minor second, notated using two adjacent letter names A semitone, also called a...
s smaller, respectively.
Its inversion is the
diminished third, and its
enharmonicIn modern music and notation, an enharmonic equivalent is a note , interval , or key signature which is equivalent to some other note, interval, or key signature, but "spelled", or named, differently...
equivalent is the
minor seventhA minor seventh is the smaller of two commonly occurring musical intervals that span seven diatonic scale degrees. The prefix 'minor' identifies it as being the smaller of the two , its larger counterpart being a major seventh. The minor seventh is abbreviated as m7 and its inversion is the major...
; In
septimal meantone temperamentIn music, septimal meantone temperament, also called standard septimal meantone or simply septimal meantone, refers to the tempering of 7-limit musical intervals by a meantone temperament tuning in the range from fifths flattened by the amount of fifths for 12 equal temperament to those as flat as...
, it is specifically equivalent to the
harmonic seventhThe harmonic seventh interval , also known as the septimal minor seventh, or subminor seventh, is one with an exact 7:4 ratio . This is somewhat narrower than and is "sweeter in quality" than an "ordinary" minor seventh, which has a just-intonation ratio of either 16:9 or 9:5, or an...
(a
just intervalIn music, just intonation is any musical tuning in which the frequencies of notes are related by ratios of whole numbers. Any interval tuned in this way is called a just interval; in other words, the two notes are members of the same harmonic series....
of 7/4).
In the tuning system known as
equal temperamentEqual temperament is a musical temperament, or a system of tuning in which every pair of adjacent notes has an identical frequency ratio. In equal temperament tunings, an interval — usually the octave — is divided into a series of equal steps...
the augmented sixth is equal to ten semitones and is a
dissonantIn music, a consonance is a harmony, chord, or interval considered stable, as opposed to a dissonance — considered unstable...
interval.
The augmented sixth is relatively rare. Its most common occurrence is built on the lowered
submediantIn music, the submediant is the sixth tonal degree of the diatonic scale. It is so called because it is a third below the tonic, in contrast to the mediant being a third above the tonic...
of the prevailing key, in which position the interval assumes a natural tendency to resolve by expanding to an
octaveIn music, an octave , is the interval between one musical pitch and another with half or double its frequency. The octave relationship is a natural phenomenon which has been referred to as the "basic miracle of music," the use of which is "common in most musical systems." It may be derived from the...
built on the
dominantIn music, the dominant is the fifth degree of a musical scale. The dominant has the role of creating instability that requires the tonic or goal-tone for release....
tonal degree. In its most common and expected resolution, the lower note of the interval moves downwards by a minor second to the dominant while the upper note, being chromatically inflected, is heard as the leading note of the dominant key, rising naturally by a minor second.
It is the strong tendency to resolve in this way that properly identifies this interval as being an augmented sixth rather than its more common enharmonic equivalent: the minor seventh, which has a tendency to resolve inwardly.
As the augmented sixth is correctly named only in certain specific contexts, the notational distinction between it and the minor seventh is often ignored. Regardless of the true diatonic context, many writers choose in favour of the more familiar minor seventh - especially in chord notation, in which chords containing it are always labelled
seventh chordA seventh chord is a chord consisting of a triad plus a note forming an interval of a seventh above the chord's root. When not otherwise specified, a "seventh chord" usually means a major triad with a flat seventh...
s.
The augmented sixth interval in combination with certain other intervals forms the group of chords known collectively as
augmented sixth chordAn augmented sixth chord contains the interval of an augmented sixth above its "root". This chord has its origins in the Renaissance, further developed in the Baroque, and became a distinctive part of the musical style of the Classical and Romantic periods....
s.