@Eorl,
Eorl wrote:
It's complicated. Just because you can't hear frequencies outside the audible range doesn't mean the presence of such frequencies won't effect what you are hearing. For example, if you add a 10hz tone and a 30hz tone to a speaker that is playing music, you'll hear a difference for a couple of reasons. The lower tone (and to some extent the high one) will produce harmonics in the audible spectrum, and the higher tone will have your speaker very busy, altering it's abililty to produce the other sounds.
I seem to remember that there is a heterodyne effect whereby two inaudible frequencies above the audible range can mix in the human ear to produce a frequency equal to their difference. There will also be a frequency equal to their sum. This difference frequency is what is known in acoustics as a "beat tone", isn't it? Also there is the binaural beat, heard (or perceived) when the right ear listens to a slightly different tone from the left ear. Here, the tones do not interfere physically, but are summed by the brain. I think some devices using one or both (or a mixture) of these techniques have been contemplated by law enforcement agencies as crowd control devices - the effect being a disturbing or painful noise with no obvious source. I should have thought therefore that the presence or otherwise of frequencies above the audible might very well influence subjective aural experiences.
