This selection comes from John Calvin's "Preface to the Psalter" (trans. Charles Garside in John Calvin: Writings on Pastoral Piety, ed. Elsie Anne Mckee [CWS; New York: Paulis, 2001], 94) You can find an on-line translation of this document here.

"And in truth we know from experience that song has great force and vigor to around and inflame people's hearts to invoke and praise God with a more vehement and ardent zeal. There must always be concern that the song be neither light nor frivolous, but have gravity and majesty, as Saint Augustine says. And thus there is a difference between the music which one makes to entertain people at table and in their homes, and the psalms which are sung in the church in presence of God and His angels."

Here, too, is a selection of Athanasius on singing from his writings on the Psalms:

When, therefore, the Psalms are chanted, it is not from any mere desire for sweet music but as the outward expression of the inward harmony obtaining in the soul, because such harmonious recitation is in itself the index of a peaceful and well-ordered heart. To praise God tunefully upon an instrument, such as well-tuned cymbals, cithara, or ten-stringed psaltery, is, as we know, an outward token that the members of the body and the thoughts of the heart are, like the instruments themselves, in proper order and control, all of them together living and moving by the Spirit's cry and breath.