Music adorns churches as well as the visual arts. Not only does Gregorian chant belong to the Church, it also belongs to the faithful:
191. As regards music, let the clear and guiding norms of the Apostolic See be scrupulously observed. Gregorian chant, which the Roman Church considers her own as handed down from antiquity and kept under her close tutelage, is proposed to the faithful as belonging to them also. In certain parts of the liturgy the Church definitely prescribes it;[Cf. Pius X, Apostolic Letter (Motu Proprio) Tra le sollectitudini] it makes the celebration of the sacred mysteries not only more dignified and solemn but helps very much to increase the faith and devotion of the congregation. For this reason, Our predecessors of immortal memory, Pius X and Pius XI, decree – and We are happy to confirm with Our authority the norms laid down by them – that in seminaries and religious institutes, Gregorian chant be diligently and zealously promoted, and moreover that the old Scholae Cantorum be restored, at least in the principal churches. This has already been done with happy results in not a few places.[Cf. Pius X, loc. cit.; Pius XI, Constitution Divini cultus, 2, 5]
By the late nineteenth century, Gregorian chant was practically extinct most everywhere outside of some monasteries. There was some progress in the early twentieth century on this front–what Pope Pius alludes to here.