21 Apr
2010
21 Apr
'10
6:47 p.m.
On Wed, Apr 21, 2010 at 4:34 PM, Rob <lau(a)kudla.org> wrote:
On Wednesday 21 April 2010 02:47 pm, micromoog wrote:
While I consider this to be an academic discussion since I have high
frequency hearing loss, it does seem to me that with a sample rate of
44.1KHz, a 22.04KHz sine wave is indistinguishable from a 22.04KHz square
wave despite being below the Nyquist frequency,
In any good system, both are going to be silence, as they've been
entirely lowpassed away.
Choosing something a little lower (like 18kHz), they'll still be
identical, as the harmonics that make a square wave a square wave will
also have been lowpassed away. The square wave's first harmonic (OK,
it's actually called the 'second harmonic, as the 'first harmonic' is
the fundamental) is at 36kHz, above Nyquist.
When you filter away all the harmonics of a square wave, what do you
get? A sine wave.
When you filter away all the harmonics of a triangle wave, what do you
get? A sine wave.
It is
easy to understand that this correlation between phase and
correct amplitude also affects frequencies below half the
sampling-rate. Might be as
low as quarter of the sampling-rate, which in case of the CD is 11kHz.
This is a
pretty bold claim, and contradicts Nyquist and other
literature. Do you have a citation for the claim that frequencies "as
low as a quarter of the sampling-rate" are damaged by sampling? It seems like a pretty esoteric thing to care about,
but if one does care
about frequencies above 11KHz, I guess he really might need to consider
sample rates higher than 44KHz.
Completely incorrect. No shred of truth, period.
The Nyquist frequency is the threshold
above which tones can't be represented at all, not the threshold below
which tones are represented with any kind of fidelity.
I grant this is an advanced a topic that relatively few people have
studied. But just because you personally don't understand it doesn't
make it 'not so'.
Monty