It's The Country and the City - chapter 2 of Culture and Society is about the romantic poets.
And Williams is writing about nostalgia for 'the organic community', not artistic declines.
Also it was a little unfair of you to snip the rest of my sentence '... within genres, and to the extent that 'the West's' music is composed of genres, possibly even in 'the West's' music as a whole.' I stressed the 'within genres' to avoid the suggestion of a transcendent perspective for criticism. Also, I was arguing against Somebody that there had not been such a decline in music in recent decades.
Mike Beggs