> Arguably pop music, as measured by the singles charts, peaked in early 1966, thereafter beginning a shallow decline in overall quality which was already steepening by 1970. While some will date this tail-off to a little later, only the soulless or tone-deaf will refuse to admit any decline at all. Those with ears to hear, let them hear.
After a couple more decades of continuing (though not uniform and consistent) overall decline, the broad truth of this looks more evident than ever. In much the same way that classical music probably peaked roughly around the death of Beethoven, with the shallow decline in overall quality becoming steeper some time in the late nineteenth to early twentieth century.