What was a recommendation of the Council of Trent regarding music for the church?

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Catholic AnswerThere was one sentence, in all the documents of the Council of Trent that addressed music, it was towards the end of the 22nd Session, which dealt with the Holy Mass: They shall also banish from churches all those kinds of music, in which, whether by the organ, or in the singing, there is mixed up any thing lascivious or impure; as also all secular actions; vain and therefore profane conversations, all walking about, noise, and clamour, that so the house of God may be seen to be, and may be called, truly a house of prayer.

In the Middle Ages, "tropes" had developed, these were additions to the chant which was native to the Latin liturgy. the Council of Trent banned them completely, although it did allow polyphony.

In the matter of music, polyphonic music was permitted in addition to the use of traditional chant as long as the texts of polyphonic pieces were not unduly obscured. Tropes were banned entirely and the sequence was suppressed except for a handful of favorites.

.Catholic AnswerThe Council of Trent was the Catholic Church's response to the disaster of the protestant revolt and the problems within the Church at that time. It was important to music as it spelled out exactly what was permitted to be celebrated in a Church and at Mass, and what was recommended (Gregorian Chant).

from the Catholic Encyclopedia article on the Council of Trent

The Ecumenical Council of Trent has proved to be of the greatest importance for the development of the inner life of the Church. No council has ever had to accomplish its task under more serious difficulties, none has had so many questions of the greatest importance to decide. The assembly proved to the world that notwithstanding repeated apostasy in church life there still existed in it an abundance of religious force and of loyal championship of the unchanging principles of Christianity. Although unfortunately the council, through no fault of the fathers assembled, was not able to heal the religious differences of Western Europe, yet the infallible Divine truth was clearly proclaimed in opposition to the false doctrines of the day, and in this way a firm foundation was laid for the overthrow of heresy and the carrying out of genuine internal reform in the Church.