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ktesibios
SFN Regular
USA
505 Posts |
 Posted - 11/14/2005 : 13:02:10 [Permalink]
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Some funny things about the human ear-brain system.
If you look at this plot of the sensitivity versus frequency of the human ear (scroll down to fig. 3.2a), you'll notice that the absolute sensitivity of our hearing is maximized around the 2 kHz area.
Our sense of pitch is most independent of loudness right in that same area:
quote:
Perceived loudness increases logarithmically with amplitude. Neural mechanisms for loudness include two layers of sensory receptors with differential sensitivity, saturation at high intensities, and changes in neural firing rate. At the same physical intensity, frequencies near the center of the audible frequency range are heard as louder than those at the low and high ends of the range. Increased loudness slightly raises the pitch of frequencies above 2,000 Hz and lowers the pitch of frequencies below 1,000 Hz, and it may affect pitch by introducing *combination tones.
http://gate.tenhauser.com/pos.html; also see Fritz Winckel's Music, Sound and Sensation
Our ability to discriminate between slightly different pitches and loudnesses is also at its best in the range above 1 Khz.
In short, our hearing acuity tends to be at its greatest right smack dab in the part of the sound spectrum which has been shown empirically to be the most critical for speech comprehension. ( See Davis & Davis, Sound System Engineering 2nd. edition or Glen Ballou, ed.,The New Audio Cyclopedia or pretty much any textbook on sound system design or psychoacoustics for more).
The adaptive value, for a species which lives in groups, of physical features which promote intra-species communication aren't hard to envisage. Other animals have their own sensory optimizations, evolved under different conditions of environment and lifestyle.
The fact that as an intelligent species we've learned to take advantage of some of the features of our acoustic perception systems for our own enjoyment isn't uch of an argument against those systems having evolved; what we know about how they perform seems to me actually an argument in favor of their having been acted upon by natural selection.
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