Make sure to click on the recent article by Dr. Charles Weaver, because he links to something remarkable. In essence, it’s a list—written by William Byrd!—regarding why we should sing.
Pope Saint Paul VI (3 April 1969): “Although the text of the Roman Gradual—at least that which concerns the singing—has not been changed, the Entrance antiphons and Communions antiphons have been revised for Masses without singing.”