MOTM

>And there's the rub.  Most people CAN distinguish between high frequency
>sines and triangles, even though the harmonics of the triangle are above
>the range of their hearing.

That's because most people who try it use a sine and triangle with 
the same peak-to-peak value, which means the amplitude of the 
fundamental is different. My recollection is that studies that 
correct for this show that, in fact, most people *can't* hear the 
difference.

>   Ultrasonic components have an effect on
>perception, even if they can't be heard.  Further proof of this is the
>"audio spotlight" that delivers audio using ultrasonics (see
>holosonics.com).

They use difference tones to derive audible frequencies from 
ultrasonic frequencies. This doesn't prove anything about ultrasonic 
perception, any more than a theremin does.

I'm open to the possibility that ultrasonic perception is real, but I 
have yet to see any convincing evidence. The closest thing is the 
notorious Oohashi study, which I don't find convincing, but some do.

>The question is, how high do you need to go to accurately reproduce a
>performance?  Horns are the acoustic instruments that produce the most
>ultrasonics, and they don't do much past 50kHz.

Gamelans and crash cymbals go up into the MHz, IIRC.
-- 


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Tim Walters : The Doubtful Palace : http://www.doubtfulpalace.com