Catechism of the Catholic Church §1156 — excerpt
"The musical tradition of the universal Church is a treasure of inestimable value, greater even than that of any other art. the main reason for this pre-eminence is that, as a combination of sacred music and words, it forms a necessary or integral part of solemn liturgy."
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: SC 112 · St. Augustine, En. in Ps. 72,1: PL 36, 914