Magic wrote:
> Well I can definately hear the difference between a triangle, square and sine
> wave at 14kHz, and I'm no fruit bat! I do have quite acute hearing though, as I
> can hear frequencies up to 25kHz, which is quite unusual - certainly surprised
> the person testing my hearing anyway!
The difference between a sine wave and a square or triangle wave is the
absence of harmonics in the sine wave. For a fundamental frequency of
14KHz, the first harmonic present in a square or triangle wave will be
one octave higher, or 28KHz. Even your somewhat un-human hearing
wouldn't hear that first harmonic or any subsequent higher order ones,
and so could not discern the difference between these wave forms. I
believe that any differences you hear are either artifacts produced by
your function generator, in which case you should throw it in the bin,
or differences in the signal levels that you are perceiving as a change
of timbre.
In the case of an audio reproduction system that faithfully records up
to 20KHz, any fundamental frequencies of above 10KHz will be reproduced
as sine waves, regardless of their original harmonic content and
resultant wave forms. Note that this is almost equally true for analog
and digital systems, except that analog systems usually have a much
shallower roll-off above their frequency cut-off point.
So what is the consequence of this? Anyone who writes for "What Hifi"
magazine will immediately hear the difference between a 44.1KHz sampling
rate and a 96KHz sampling rate, because their favourite 18KHz square
wave sound will still be somewhat square when it is reproduced. Us
mortals however that failed to respond to the 36KHz harmonic due to our
colour-blindness will be somewhat dazzled by the "What Hifi" scribe and
his uncanny ability to hear the difference after a quick
non-colour-blind visual check of the source.
-cb
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