Barbershop harmony is a style of unaccompanied singing in which three voices harmonize to a melody. The voice parts are called tenor, lead, baritone, and bass.
The lead usually sings the melody. The tenor harmonizes above the melody. The bass sings the lowest harmonizing notes, and the baritone provides in between notes, either above or below the lead, completing the chords that give barbershop its distinctive, four part sound.
The style is further identified by the use of chords that are harmonious (pleasing). Tuning is as nearly perfect as is vocally possible. The style is distinguished by uniformity of word sounds and a special emphasis on close harmony.
Music is in the style of "the old songs" from the heyday of Tin Pan Alley, circa 1890 1910. Melodies are in the vocal and skill range of the average singer. Lyrical emphases are on simple, heartfelt emotion: love, friendship, mother, moon and June and the girl next door.
Technically speaking, barbershop music features major and minor chords and barbershop (dominant type) seventh chords, resolving primarily on the circle of fifths. (At least 35 percent of the chords are barbershop seventh chords.) Sixth, ninth, and major seventh chords are avoided except where demanded by the melody, while chords containing the minor second interval are not used.
The basic harmonization may be embellished with additional chord progressions to provide harmonic interest and rhythmic momentum, to carry over between phrases, or to introduce or close the song effectively.
Barbershop interpretative style permits relatively wide liberties in the treatment of note values staying within proper musical form and uses changes in tempo and volume to more effectively create a mood and tell a story artistically.
Relative to an established sense of tonality, the melody line and the harmony parts are enharmonically adjusted in pitch to produce an optimum consonant sound. The resulting pitch relationships are often considerably at variance with those defined by the equal temperament of fixed pitch instruments.
Use of similar word sounds in good quality and optimum volume relationships by each of the voice parts further enhances the sensation of consonance by mutual reinforcement of the harmonics (overtones) to produce the unique full or expanded sound characteristic of barbershop harmony.