Barbershop seventh chord
The harmonic seventh chord is a major triad plus the harmonic seventh interval (ratio of 7:4, about 968.826 cents). This interval is somewhat narrower (about 48.77 cents flatter, a septimal quarter tone) and is "sweeter in quality" than an "ordinary"minor seventh, which has a just intonation ratio of 9:5 (1017.596 cents), or an equal-temperament ratio of 1000 cents (25⁄6:1). 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 chord. 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).
A frequently encountered example of the harmonic seventh chord is the last word of the "...and many more!" modern addition to the song "Happy Birthday to You" When sung by professional singers, the harmony on the word "more" typically takes the form of a harmonic seventh chord.
The alpha scale has, "excellent harmonic seventh chords...using the inversion of 7:4, i.e., 8/7."
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