[plug]audio cds, was slowdown probs

[Mike]

At 09:25 PM 23/8/2001 +0800, you wrote:

>you shouldnt be able to hear a 27khz sine wave, but you can notice a slight 
>difference in the sound of a 9khz square wave over a sine wave. i dont know 
>why , but if someone with more knowledge about human hearing can fill us in 
>on this , it would be appreciated. 

9KHz square wave is same as 9KHz sine wave + harmonics (even) IIRC
and the ear 'recognises' these harmonics as distortions from the
pure 9KHz sinewave equivalent,

It is actually possible for the human ear to be aware of frequencies
far higher then 20KHz. It depends on a number of factors, from what
I recall of the physics - the hairs in the cochlea can go into
sympathetic resonance if stimulated with frequencies a multiple
higher then their normal sensitivity. The only problem is the power
levels need to be very high and the ears capacity to discriminate
falls off considerably.

ie. 20Hz to 20KHz (for a 12yr old) is a fairly continuous log response
20KHz and up is extremely discontinuous. With enough power you might
hear 40KHz and 45KHz or rather - sense its presence - but not at
say 41KHz to 44KHz since those frequencies might not cause the
sympathetic resonance.

Finding a tweeter that gives out enough power at 40Khz might also
be hard to find and you wouldn't want to try it anyway - as you
could damage your hearing and not actually hear anything in the
process !



Kind Regards  ~`:o)

Mike Massen
Network Power Systems
Perth, Western Australia  Ph/Fx +61 8 9444 8961 

Power system in Jungle, Twin tyre car, Differential gauge
http://members.iinet.net.au/~erazmus/index.html

Some say there is no magic but, all things begin with thought then it becomes
academic, then some poor slob works out a practical way to implement all that
theory, this is called Engineering - for most people another form of magic.