I’m happy to report that the legislative ground has just shifted, and dramatically so. The new translation of the General Instruction removes the discretion from the music team to sing pretty much whatever it wants. The new text, which pertains to the new translation of the Missal that comes into effect on Advent this year, makes it clear beyond any doubt: the music of the Mass is the chanted propers of the Mass. There are options but these options all exist within the universe of the primary normative chant. There can be no more making up some random text, setting it to music, and singing it as the entrance, offertory, or communion.This isn't a big deal for our parish, or at least for most of the Masses at our parish. Heck, the Saturday vigil has a men's choir already doing chant. Although I could foresee a weaning process for our 9 a.m. Sunday family mass. It is all very tastefully done, but it has the most "modern" music.
Jeffrey Tucker, The Chant Cafe
Read more at The Chant Cafe where they have a comparison of the old and new as well as some commentary. (Via New Advent.)