To appease your troubled mind:
Instruction on Sacred Music in the Liturgy (Prot. 0)
March 5, 1967
Sacred Congregation of Rites
"28. The distinction between solemn, the high, and the low Mass, sanctioned by the 1958 Instruction (no. 3) remains in force, according to tradition and current law. But for pastoral reasons degrees of solemnity for the sung Mass are proposed here in order that it will become easier, in accord with each congregation’s capability, to make the celebration of Mass more solemn through the use of singing.
These degrees must be so employed, however, that the first may always be used without the others, but the second and third never without the first. Thus in all cases the faithful are to be brought to take part fully in the singing.
To the first degree belong:
a. in the entrance rites
-the priest's greeting and the congregation's response;
-the opening prayer.
b. in the liturgy of the word
-the gospel acclamations.
c. in the liturgy of the eucharist
-the prayer over the gifts;
-the preface, with the opening dialogue and the Sanctus;
-the Lord's Prayer, with the invitation and embolism;
-the greeting May the peace of the Lord;
-the prayer after communion;
-the final dismissal.
To the second degree belong:
a. Kyrie, Gloria, Agnus Dei;
b. profession of faith;
c. general intercessions.
To the third degree belong:
a. songs for the entrance procession and for communion;
b. chants after a lesson or epistle;
c. Alleluia before the gospel;
d. songs for the presentation of the gifts;
e. the Scripture readings, except when it seems better not to have them sung.
take notice on number 31 d.
“9. The choice of the style of music for a choir or congregation should be guided by the abilities of those who must do the singing. The Church does not exclude any type of sacred music from liturgical services as long as the music matches the spirit of the service itself and the character of the individual parts and is not a hindrance to the required active participation of the people.”
Hope it helps!