What does Augustine mean by the "hymns and psalms" which were introduced into the liturgy?

I am puzzling over a passage in Augustine's *Confessions*, where he speaks of himself and his mother in the Church at Milan: > We were still cold, untouched by the warmth of your Spirit, but were > excited by the tension and disturbed atmosphere in the city [of > Milan]. That was the time when the decision was taken to introduce > hymns and psalms sung after the custom of the Eastern Churches, to > prevent the people from succumbing to depression and exhaustion. From > that time to this day the practice has been retained and many, indeed > almost all your flocks, in other parts of the world have imitated it. > (*Confessions* 9.7.15, trans. Chadwick, p. 165) A few things seem strange: (1) Augustine has already been baptized by this point, and yet he calls himself "untouched by ... your Spirit"; (2) surely singing in Church had existed long before Augustine; and (3) surely Augustine believed that the purpose of singing hymns was to worship God, as opposed to keeping the congregation from "depression and exhaustion." What is the historical context of the "hymns and psalms" which were introduced? Do we know what Eastern tradition Augustine is talking about here? And, in general, what is the meaning of this passage?