50. On the other hand, when I avoid very earnestly this kind of deception, I err out of too great austerity. Sometimes I go to the point of wishing that all the melodies of the pleasant songs to which David’s Psalter is adapted should be banished both from my ears and from those of the Church itself. In this mood, the safer way seemed to me the one I remember was once related to me concerning Athanasius, bishop of Alexandria, who required the readers of the psalm to use so slight an inflection of the voice that it was more like speaking than singing.
However, when I call to mind the tears I shed at the songs of thy Church at the outset of my recovered faith, and how even now I am moved, not by the singing but by what is sung (when they are sung with a clear and skillfully modulated voice), I then come to acknowledge the great utility of this custom. Thus I vacillate between dangerous pleasure and healthful exercise. I am inclined--though I pronounce no irrevocable opinion on the subject--to approve of the use of singing in the church, so that by the delights of the ear the weaker minds may be stimulated to a devotional mood. Yet when it happens that I am more moved by the singing than by what is sung, I confess myself to have sinned wickedly, and then I would rather not have heard the singing. See now what a condition I am in! Weep with me, and weep for me, those of you who can so control your inward feelings that good results always come forth. As for you who do not act this way at all, such things do not concern you. But do thou, O Lord, my God, give ear; look and see, and have mercy upon me; and heal me--thou, in whose sight I am become an enigma to myself; this itself is my weakness.
Howard L. Rice & James C. Huffstutler, Reformed Worship, pp. 103-104:
What were the effects or impact of Calvin's psalm singing? A letter from a young man from Antwerp, who had sought refuge in Strasbourg during Easter week of 1545, indicates what it meant for some to hear the Psalms sung in their own language:On Sundays...we sing a psalm of David or some other prayer taken from the New Testament. The psalm or prayer is sung by everyone together, men as well as women, with a beautiful unanimity, which is something beautiful to behold. For you must understand that each one has music book in his hand; that is why they cannot lose touch with one another. Never did I think that it could be as pleasing and delightful as it is. For five or six days at first, as I looked upon this little company, exiled from countries everywhere for having upheld the honor of God and His gospel, I would begin to weep, not at all from sadness, but from joy at hearing them sing so heartily, and, as they sang, giving thanks to the Lord that he had led them to a place where His name is honored and glorified. No one could believe the joy which one experiences when one is singing the praises and wonders of the Lord in the mother tongue as one sings them here.