In Canto Four of his poem John Shade (the poet in VN’s novel Pale Fire, 1962) mentions “a sustained low hum of harmony:”
Gently the day has passed in a sustained
Low hum of harmony. The brain is drained
And a brown ament, and the noun I meant
To use but did not, dry on the cement.
Maybe my sensual love for the consonne
D'appui, Echo's fey child, is based upon
A feeling of fantastically planned,