Harmonic seventh
From Wikipedia, the free encyclopedia
The harmonic seventh interval, also known as the "blue seventh" or "septimal minor seventh"[1], is one with an exact 7:4 ratio (about 969 cents).[2] This is somewhat less than a minor seventh, which has a just-intonation ratio of either 16:9 or 9:5, or an equal-temperament ratio of 1000 cents.
The harmonic seventh chord is a major triad plus the above-mentioned harmonic seventh interval.
Frequent use of this chord is one of the defining characteristics of blues and barbershop harmony; barbershoppers refer to it as "the barbershop seventh." Since barbershop music tends to be sung in just intonation, the barbershop seventh chord may be accurately termed a harmonic seventh chord.
The harmonic seventh chord is also widely used in "blues flavored" music. As guitars, pianos, and other equal-temperament instruments cannot play this chord, it is frequently approximated by a dominant seventh (see above). As a result it is often called a dominant seventh chord and written with the same symbols (such as the blues progression I7 - V7 - IV7).
The harmonic seventh note is about a quarter-tone flatter than an equal tempered minor seventh. When this flatter seventh is used, the dominant seventh chord's "need to resolve" down a fifth is weak or non-existent. This chord is often used on the tonic (written as I7) and functions as a "fully resolved" final chord.[3]
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| By Type | Triad | Major · Minor · Augmented · Diminished · Suspended |
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| Seventh | Major · Minor · Dominant · Diminished · Half-diminished · Minor-major · Augmented major · Augmented minor | |
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| Extended | Ninth · Eleventh · Thirteenth | |
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| Other | Sixth · Augmented sixth · Altered · Added tone · Polychord · Quartal and quintal · Tone cluster · Power | |
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| By Function | Diatonic | Tonic · Dominant · Subdominant · Submediant |
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| Altered | Borrowed · Neapolitan chord · Secondary dominant | |
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| With Names | Elektra chord · Hendrix chord · Mystic chord · Petrushka chord · Tristan chord · So What chord | |
