Originally Posted by
Opti-cal
I have a love/hate relationship with scientific "facts".
We use facts indefinitely to build systems based on scientific theory. They help us understand how sound travels from recording format via source and through various amplification stages into your speakers/headphones.
However these "facts" don't really explain the effects these frequencies, that apparently cannot be heard, have on your brain. You certainly do not have to "hear" the frequencies for them to have an effect on your "hearing/portrayal" (and therefore your appreciation) of the music.
As others have eluded to sub bass frequencies are felt and ultrasonic ones perceived (they can also break glass etc). Also consider the effects these frequencies have on the rest of the recording.
We may not hear them but they may have some effect on other notes that were being recorded at the same time. I'm speculating in this previous sentence but having mixed digital music in the past I can tell you that sometimes removing what technically a human ear cannot detect in a recording, can effect that recording in both positive and negative ways.
I've also attempted to "clean up" ambient, live recordings and sometimes the silence (which often has detectable noise well above 15k) when removed, again, removes something more from the recording.
Plus think how devastated our K9 friends would be if we started cutting off the extra frequencies in our favorite albums, they expect to hear them!!