The following excerpt comes to us by way of FSSP.la :
It’s taken from a talk given recently by Fr. Dominic Popplewell, FSSP, who went on to trace the various ways “liturgy” was used in the early Church and by the Sacred Scriptures.
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.”