The harmonic seventh intervalplay(help·info), also known as the septimal minor seventh[1], is one with an exact 7:4 ratio (about 969 cents).[2] This is somewhat less than and is "sweeter in quality" than an "ordinary"[3]minor seventh, which has a just-intonation ratio of either 16:9[3] or 9:5[4], or an equal-temperament ratio of 1000 cents.
The harmonic seventh chordplay(help·info) 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.[citation needed] As guitars, pianos, and other equal-temperament instruments cannot play this chord, it is frequently approximated by a dominant seventh. 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 differs from the augmented sixth by 224/225, or about a 1/3 of a comma[5]. 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.[6]
An often heard example of the harmonic seventh chord is the last word of the modern addition to the song "Happy Birthday to You", with the lyrics, "and many more!" The harmony on the word "more" is typically sung as a harmonic seventh chord.[7]
^ Bosanquet, Robert Holford Macdowall (1876). An elementary treatise on musical intervals and temperament, pp. 41-42. Diapason Press; Houten, The Netherlands. ISBN 90-70907-12-7.
^ ab "On Certain Novel Aspects of Harmony", p.119. Eustace J. Breakspeare. Proceedings of the Musical Association, 13th Sess., (1886 - 1887), pp. 113-131. Published by: Oxford University Press on behalf of the Royal Musical Association.
^ "The Heritage of Greece in Music", p.89. Wilfrid Perrett. Proceedings of the Musical Association, 58th Sess., (1931 - 1932), pp. 85-103. Published by: Oxford University Press on behalf of the Royal Musical Association.
^ "On Some Points in the Harmony of Perfect Consonances", p.153. R. H. M. Bosanquet. Proceedings of the Musical Association, 3rd Sess., (1876 - 1877), pp. 145-153. Published by: Oxford University Press on behalf of the Royal Musical Association.
^ Mathieu, W.A. (1997). Harmonic Experience, pp. 318-319. Inner Traditions International; Rochester, Vermont. ISBN 0-89281-560-4.
