# Re: High-frequency hearing in humans

So, the distance to familiar broad band sound sources could be judged very quickly - eg. while they are moving.
A chart of the 1db reduction to distance should give an approximate minimum effective range for these observations.
Well played Tony!
Dave

-----Original Message-----
From: Antonio Miller <antonio.miller@xxxxxxxxx>
To: AUDITORY@xxxxxxxxxxxxxxx
Sent: Wed, Jan 26, 2011 4:31 pm
Subject: Re: [AUDITORY] High-frequency hearing in humans

```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?

-Tony

[1] http://en.wikibooks.org/wiki/Engineering_Acoustics/Outdoor_Sound_Propagation#endnote_HandbookofAcoustics1998
[2] Air @ 1 atm, 20deg C, 50% relative humidity.

On Tue, Jan 25, 2011 at 4:27 AM, Piotr Majdak <piotr@xxxxxxxxxx> wrote:
> Dear list,
>
> I'm looking for the reasons for the good high-frequency* hearing  in humans.
>
> The reasons I have until now are actually the obvious ones:
> * Pinna localization cues
> * Interaural level cues (ILD, they actually start to work from around 2 kHz)
>
> What do you think: if there were no need for the ILD and pinna cues, would
> there be any other reasons?
>
> Thanks,
>
> Piotr
> *) say, above 8 kHz
>
> --
> Piotr Majdak
> Psychoacoustics and Experimental Audiology
> Acoustics Research Institute <http://www.kfs.oeaw.ac.at>
> Austrian Academy of Sciences <http://www.oeaw.ac.at/>
> Wohllebengasse 12-14, 1040 Vienna, Austria
> Tel.: +43 1 51581-2511
> Fax: +43 1 51581-2530
>
```