Barbershop music in tags or codas, or when some appropriate embellishment can be created. One characteristic feature of barbershop harmony is the use of what is known as "snakes" and "swipes." This is when a chord is altered by a change in one or more non-melodic voices. Occasional passages may be sung by fewer than four voice parts. Barbershop music is generally performed by either a barbershop quartet, a group of four singers with one on each vocal part, or a barbershop chorus, which closely resembles a choir with the notable exception of the genre of music. According to the Barbershop Harmony
Barbershop music Society (BHS), "Barbershop music features songs with understandable lyrics and easily singable melodies, whose tones clearly define a tonal center and imply major and minor chords and barbershop (dominant and secondary dominant) seventh chords that resolve primarily around the circle of fifths, while making frequent use of other resolutions." Slower barbershop songs, especially ballads, often eschew a continuous beat, and notes are often held (or sped up) ad libitum. Except for the bass, the voice parts in barbershop singing do not correspond closely to their classical music counterparts; the tenor range and tessitura are similar to those of the classical