Excerpted from the USCCB site.

http://www.usccb.org/prayer-and-worship/the-mass/general-instruction-of-the-roman-missal/girm-chapter-2.cfm

The Italics are mine, highlighting some issues that would at times vary from what I and possibly others new to this have believed to the intent of the GIRM...and possibly why there has been confusion.

For example, while the Communion Chant is mentioned, later it is described as the chant after communion.



The Prayers and Other Parts Pertaining to the Priest

30. Among those things assigned to the Priest, the prime place is occupied by the Eucharistic Prayer, which is the high point of the whole celebration. Next are the orations, that is to say, the Collect, the Prayer over the Offerings, and the Prayer after Communion. These prayers are addressed to God by the Priest who presides over the assembly in the person of Christ, in the name of the entire holy people and of all present.[43] Hence they are rightly called the “presidential prayers.”

31. Likewise it is also for the Priest, in the exercise of his office of presiding over the gathered assembly, to offer certain explanations that are foreseen in the rite itself. Where this is laid down by the rubrics, the celebrant is permitted to adapt them somewhat so that they correspond to the capacity for understanding of those participating. However, the Priest should always take care to keep to the sense of the explanatory text given in the Missal and
to express it in just a few words. It is also for the presiding Priest to regulate the Word of God and to impart the final blessing. He is permitted, furthermore, in a very few words, to give the faithful an introduction to the Mass of the day (after the initial Greeting and before the Penitential Act), to the Liturgy of the Word (before the readings), and to the Eucharistic Prayer (before the Preface), though never during the Eucharistic Prayer itself; he may also make concluding comments regarding the entire sacred action before the Dismissal.

32. The nature of the “presidential” parts requires that they be spoken in a loud and clear voice and that everyone listen to them attentively.[44] Therefore, while the Priest is pronouncing them, there should be no other prayers or singing, and the organ or other musical instruments should be silent.

33. For the Priest, as the one who presides, expresses prayers in the name of the Church and of the assembled community; but at times he prays only in his own name, asking that he may exercise his ministry with greater attention and devotion. Prayers of this kind, which occur before the reading of the Gospel, at the Preparation of the Gifts, and also before and after the Communion of the Priest, are said quietly.

Other Formulas Occurring during the Celebration

34. Since the celebration of Mass by its nature has a “communitarian” character,[45] both the dialogues between the Priest and the assembled faithful, and the acclamations are of great significance;[46] for they are not simply outward signs of communal celebration but foster and bring about communion between Priest and people.

35. The acclamations and the responses of the faithful to the Priest’s greetings and prayers constitute that level of active participation that is to be made by the assembled faithful in every form of the Mass, so that the action of the whole community may be clearly expressed and fostered.[47]

36. Other parts, most useful for expressing and fostering the active participation of the faithful, and which are assigned to the whole gathering, include especially the Penitential Act, the Profession of Faith, the Universal Prayer, and the Lord’s Prayer.

37. Finally, among other formulas:

a) Some constitute an independent rite or act, such as the Gloria in excelsis (Glory to God in the highest), the Responsorial Psalm, the Alleluia and Verse before the Gospel, the Sanctus (Holy, Holy, Holy), the Memorial Acclamation, and the chant after Communion;

b) Others, on the other hand, accompany some other rite, such as the chants at the Entrance, at the Offertory, at the fraction (Agnus Dei, Lamb of God) and at Communion.

The Manner of Pronouncing the Different Texts

38. In texts that are to be pronounced in a loud and clear voice, whether by the Priest or the Deacon, or by a reader, or by everyone, the voice should correspond to the genre of the text itself, that is, depending upon whether it is a reading, a prayer, an explanatory comment, an acclamation, or a sung text; it should also be suited to the form of celebration and to the solemnity of the gathering. Consideration should also be given to the characteristics of different languages and of the culture of different peoples.

Therefore, in the rubrics and in the norms that follow, words such as “say” and “proclaim” are to be understood either of singing or of reciting, with due regard for the principles stated here above.

The Importance of Singing

39. The Christian faithful who come together as one in expectation of the Lord’s coming are instructed by the Apostle Paul to sing together Psalms, hymns, and spiritual canticles (cf. Col 3:16). Singing is the sign of the heart’s joy (cf. Acts 2:46). Thus St. Augustine says rightly, “Singing is for one who loves,”[48] and there is also an ancient proverb: “Whoever sings well prays twice over.”

40. Great importance should therefore be attached to the use of singing in the celebration of the Mass, with due consideration for the culture of peoples and abilities of each liturgical assembly. Although it is not always necessary (e.g., in weekday Masses) to sing all the texts that are in principle meant to be sung, every care should be taken that singing by the ministers and the people not be absent in celebrations that occur on Sundays and on Holydays of Obligation.

However, in the choosing of the parts actually to be sung, preference is to be given to those that are of greater importance and especially to those which are to be sung by the Priest or the Deacon or a reader, with the people replying, or by the Priest and people together.[49]

41. The main place should be given, all things being equal, to Gregorian chant, as being proper to the Roman Liturgy. Other kinds of sacred music, in particular polyphony, are in no way excluded, provided that they correspond to the spirit of the liturgical action and that they foster the participation of all the faithful.[50]

Since the faithful from different countries come together ever more frequently, it is desirable that they know how to sing together at least some parts of the Ordinary of the Mass in Latin, especially the Profession of Faith and the Lord’s Prayer, according to the simpler settings.[51]