The choir is a group of singers, who sing sometimes in unison, sometimes  in 4-part harmony. Generally, the highest harmony part is soprano (when sung by women or girls) or treble (when sung by boys). The next part is alto, still written on the treble clef. The next part is tenor, sung by men and written on the bass clef in hymn books, but written on the treble clef at one octave above true pitch for most other choral music.  The deepest part is the bass, which is always written in the bass clef.

Choirs date back to ancient history, they are described by the Greek writer Homer in 850 BC.  Before the renaissance, most choral singing was monophonic, that is all voices sang in unison. Church choirs consisted of men and boys only, as women were prohibited from participating by the church authorities.

Polyphonic music for choirs with 4 or more parts reached a peak with Palestrina in the renaissance  In the classical period there was a revival of baroque choral music, and town and village choirs sprang up to sing Handel's choral works, especially the Messiah. These choirs most definitely did include women! Such amateur choirs flourish today, singing a broad variety of music including  Gilbert and Sullivan's operettas, popular musicals such as Oklahoma, as well as the traditional choral favourites such as the Bach and Handel oratorios.

General midi supplies two pseudo-voice "INSTRUMENTS",   choir ahs (Midi instrument number 52) is an approximation to the sound of the higher voices, usually female.  Voice oohs (Midi instrument number 53) is an approximation to the sound of male voices.