The proper time for the chanting of the Communion antiphon is while the priest is receiving the holy Eucharist. But if the faithful are also to go to Communion the antiphon should be sung while they receive. If this antiphon, too, is taken from a psalm, additional verses of this psalm may be sung. In this case, too, the antiphon is repeated after each, or every second verse of the psalm; when distribution of Communion is finished, the psalm is closed with the Gloria Patri, and the antiphon is once again repeated. If the antiphon is not taken from a psalm, any psalm may be used which is suited to the feast, and to this part of the mass.
After the Communion antiphon is sung, and the distribution of Communion to the faithful still continues, it is also permitted to sing another Latin song [cantiunculam] in keeping with this part of the Mass. (DMS 27c)
I would venture to say that most of us nowadays never sing for Masses at which only the celebrant makes his Communion
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