http://home.earthlink.net/~mercmoon/hoffmanint.htm

People would be surprised if
they had a meter hooked up to their system and could see that on 90% of their records and
discs, above 9500K, there's nothing there. What you're hearing up there is tape hiss, or
some other thing that isn't part of the music. When you extend everything up to that
range, there's nothing up there but noise.