Pg. 35 The Sound Machine.
"..there is another note-a vibration if you like, but I prefer to think of it as a note. You can't hear that one either. And above that there is another and another rising up the scale for ever and ever and ever, and endless succession of notes... an infinity of notes....... and on and on, higher and higher, as far as numbers go, which is... infinity... eternity... beyond the stars."