THE microphones and speakers attached to office PCs could form the heart of a
cheap, wireless network. While the computers communicate by exchanging squawks,
people won’t hear a thing from the chattering hardware, according to its
inventors.
A sound pitched slightly higher and quieter than normal conversation is
inaudible if it is only a few milliseconds long, explains John Harris, an
engineer at the University of Florida in Gainesville. Although people are good
at hearing frequencies between 1 and 20 kilohertz, we find sounds in this range
harder to hear when they are very short-lived.
Unlike directional ultrasound or infrared…
