Vocal harmony is a style of vocal music in which a consonant note or notes are simultaneously sung as a main melody in a predominantly homophonic texture. Vocal harmonies are used in many subgenres of European art music, including Classical choral music and opera and in the popular styles from many Western cultures ranging from folk songs and musical theater pieces to rock ballads. In the simplest style of vocal harmony, the main vocal melody is supported by a single backup vocal line, either at a pitch which is above or below the main vocal line, often in thirds or sixths which fit in with the chord progression used in the song. In more complex vocal harmony arrangements, different backup singers may sing two or even three other notes at the same time as each of the main melody notes, mostly with consonant, pleasing-sounding thirds, sixths, and fifths (although dissonant notes may be used as short passing notes).