General Instruction on the Roman Missal 2003

The cantor of the psalm is to sing the psalm or other biblical song that comes between the readings. To fulfill their functioncorrectly, these cantors should possess singing talent and anaptitude for correct pronunciation and diction. (Par 102)

There should be a cantor or a choir director to lead and sustain the people in the singing. When in fact there is no choir, it is up to the cantor to lead the various songs, and the people take part in the way proper to them. (Par 105)