Chuck Norcutt wrote:
> Why?
>
See! I knew I was smart to suggest that someone else explain the math. :-)
Without doing the math, simply imagine what frequency sine wave goes
from bottom to top in a short enough time to look like it goes straight
up compared to the gradual rise of a 20kHz sine wave.
Or conversely, imagine what a 20kHz square wave looks like after passing
through a 20kHz bandwidth filter. It no longer has anything like a
square shape.
The point is that, although no music may have frequencies about 20kHz,
the shape of many musical tones are far from a sine wave, and require a
wider bandwidth to be passed without being distorted. It's not that one
wants to reproduce square waves, but that they are a good general stand
in for complex musical waveforms when testing equipment. If it can pass
a 20kHz square wave with minimal rounding of the top edge and minimal
ringing behind it, it will do a good job on music of any sort.
Before you ask why our reproduction equipment doesn't need to have
160kHz bandwith, I'll say I don't know the whole answer, although a lot
of high end audio equipment does have extended frequency response.
Part of the answer is in what I said before about the net bandwidth
being a complex function of the bandwidths of all the links in the
chain. If all the production gear is very high bandwidth, the result is
better sound through even lesser bandwidth reproduction gear than if the
source gear is also of limited bandwidth.
Remember, I only got into this to draw an analogy to photographic
bandwidths and show how it isn't the weakest link (paper print
technology, in the case at hand) that determines the quality.
Moose
> Chuck Norcutt
>
> Ken Norton wrote:
>
>
>> It takes 160kHz of bandwidth to pass a a 20kHz square wave. Only 20kHz to
>> pass a 20kHz sine wave.
>>
--
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