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Re: High-frequency hearing in humans

On 26 Jan 2011 at 17:28, Antonio Miller wrote:

> We'll see if someone tears this argument apart, but you got me thinking...
> The propagation of sound in the atmosphere is pretty complicated [1],
> but some simplified calculations might be relevant to this question.
> Attenuation of sound in Air at 100m [2]:
> f<2kHz, less than 2dB
> f=4kHz, 3dB
> f=8kHz, 10dB
> f=16kHz, 36dB
> A (very rough) calculation for a detection radius of a sound that is
> 20dB above hearing threshold:
> 56m for 16kHz
> 200m for 8kHz
> 667m for 4kHz
> Meaning, you would have to be almost four times closer to the 16kHz
> sound to detect it as the 8kHz sound.  Assuming the 8 and 16kHz sound
> are equally biologically relevant, I would tend to weight the
> information content of the 16kHz sound much higher due to it's
> relative spatial scarcity.  Does that make sense to anyone?  Maybe the
> ability to hear higher frequency sounds helps lend a competitive
> advantage because they only exist within short distances of the sound
> source?

My guess would be that spatial scarcity is not as important 
as the fact that high frequency sounds are associated with 
events like twigs snapping, grass rustling, etc, which 
might indicate a nearby predator or prey.  (I don't think 
predators emit low-frequency purring while they are 

But now that you mention it, it might be very handy that 
these snaps and rustles have a limited range, since we 
don't want to get false positives from every leaf that 
falls in the forest!

Best regards,

Bob Masta
            D A Q A R T A
Data AcQuisition And Real-Time Analysis
Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!