That would be an excellent research project for someone in college studying sacred music.
In the meantime, there is a transcript of a lecture presented by Papa Ratzinger (before he was pope) at the Eighth International Church Music Congress in Rome in 1985, that appears in Adoremus Online Edition (Vol XIV, No. 2; 2008) entitled "Liturgy and Sacred Music". It probably sums up his entire philosophy on the subject. He also addressed the topic in The Spirit of the Liturgy.
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