cultural and religious life altar boy ( see above ) choir boy designates a boy ( always a minor ) singer in a choir ; here applies a specific physiological , artistically relevant criterion : they remain a musical category of their own ( boy soprano , also known as a treble ) until their voice ` breaks ' , during puberty , to join one of the adult male voice register ( countertenor ( closest to treble ) , alto , tenor , baritone , or bass ) ; only the castrato may ( not guaranteed ) remain a soprano as an adult man ; historically the term was designed for all-male ( mainly church ) choirs , with men with already broken voices ( often former choir boys ) , in modern times it also applies to mixed choirs .