MS 10-12

10. It is advisable that there be as much suitable variety as possible in the forms of celebration and the degree of participation in proportion to the solemnity of the day and of the assembly, in order that the faithful will more willingly and effectively contribute their own participation.

Long sentence. Read it a couple more times. It may be a little less confusing if it looks like this:

"Much suitable variety in:

1) the forms of celebration

and

2) the degree of participation

in proportion to:

1) the solemnity of the day

and

2) of the assembly

so that:

the congregation will more willingly and effectively participate."

Or maybe it's just as confusing this way:)

11. The real solemnity of a liturgical service, it should be kept in mind, depends not on a more ornate musical style or more ceremonial splendor but on a worthy and reverent celebration. This means respect for the integrity of the rites, that is, carrying out each of the parts in keeping with its proper character. More ornate styles of singing and greater ceremonial splendor are obviously sometimes desirable, when they are possible. But it would be in conflict with the genuine solemnity of a liturgical service if such things were to cause any element of the service to be omitted, altered, or performed improperly.

A "worthy and reverent celebration" is brought about by "respect for the integrity of the rites."

12. The Apostolic See alone has authority to establish, in accord with the norms of tradition and particularly of the Constitution on the Liturgy, those general principles that stand as the foundation for sacred music. The various lawfully-constituted territorial bodies of bishops and the bishops themselves have authority to regulate sacred music within the already defined limits. [9]

Answers the question, "So who's in charge here?"

9. See Sacrosanctum Concilium art. 22