[GreenKeys] Incredible . . .

[Bob Camp]

Hi

I always wondered if there was a reason why the results came out so 
oddly on a Teletype machine. I guess there is a reason.

	Thanks!

		Bob


On Oct 21, 2004, at 3:15 AM, Craig Sawyers wrote:

>> Sound and the perception of sound is a very complex subject.
>>
>> If you really want to go crazy take a real piece of gear like a
>> Teletype machine and do a full spectrum audio snapshot. Then mask off
>> the result with the various common filters.
>
> The ear has its own filtering mechanism, interestingly enough.  The 
> three
> bones in the inner ear (whose function is essentially a mechanical 
> impedance
> matcher between the air and liquid) have two tiny muscles attached - 
> the
> tensor timpani and the stapedius muscles.  These are acutally actuated 
> under
> different circumstances, and essentially lock the mechanism to 
> attenuate the
> sound.  This generally occurs above 70dB, and when you speak (like 
> sidetone
> suppression in telephones).
>
> But for repetitive percussive sounds, like a pile driver, the brain 
> locks
> into the repetition frequency of the thuds and *only* tightens the 
> muscles a
> fraction of a second before the next thud - then relaxes again so that 
> you
> can hear quiet noises in between the thuds.
>
> Since the clattering of a teletype has a particularly percussive 
> structure,
> those tiny muscles are probably constantly twitching (their response 
> time is
> 40ms), so changing the frequency structure of the sound might have 
> quite
> unpredictable psycho-acoustic consequences.
>
> Damned cunning....
>
> Craig
>
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