A
aetratus
Guest
As my dearest says, “If God gave you a good voice, sing loudly in church to thank him for it. If he gave you a bad voice, sing loudly in church to remind him of it.” 
I agree with this. God gives us all different talents. Also, those who sing badly and are never told(nicely) may be keeping those who do have the gift of song from using it.There are other ways those who can not sing may serve.
Ah! You saved me the trouble of looking it up.The following excerpt comes from the church document “Music in Catholic Worship”: “…Although a cantor cannot enhance the service of worship in the same way as a choir, a trained and competent cantor can perform an important ministry by leading the congregation in common sacred song and in responsorial singing.” (#35)
The following excerpt comes from another church document titled “Liturgical Music Today”: “Among music ministers, the cantor has come to be recognized as having a crucial role in the development of congregational singing. Besides being qualified to lead singing, he or she must…” (#68)
Thus, the cantor must be musically trained, competent, and qualified to perform their duties.