🚀 go-pugleaf

In article <D04gX2w163w@shark.cs.fau.edu>, terryb.bbs@shark.cs.fau.edu (terry bohning) writes:
> north@manta.NOSC.MIL (Mark H. North) writes:
> > >     i.e. If you have a 60HZ sine wave, and you sample at 120HZ, you're
> > >only going to get two points per cycle.

> > And imagine that those two points are phased such that they land at the
> > zero crossing of the 60Hz signal. All your samples are zero! This is
> > why you must sample at greater than 2nu.

> The catch is that you *know* you're sampling the highest input freq at
> 2 points per cycle.  That is, the input signal is bandlimited.  So if
> someone gives you a set of all zero samples and you know the sample
> rate is 120 Hz, the only frequency it can be is 60 Hz.

Or 0 Hz.  And supposing the signal you sampled *was* 60 Hz.  You have no
magnitude information.  You cannot reconstruct.

> The Nyquist theorem is at least, not greater than. Oppenheim & Schafer,
> "Digital Signal Processing", Prentice-Hall, 1975, pg. 28 bottom.

Yes.  They say "at least twice the highest frequency".  But the equation
they give is not ambiguous:  Wmax < pi/Tsample (or, 2*Wmax < Wsample)
(same page).

Terry, please be very careful of misinformation.

Best regards,
ruck.
-- 
John R Ruckstuhl, Jr	ruck%sphere@cis.ufl.edu, sphere!ruck
University of Florida 	ruck@cis.ufl.edu, uflorida!ruck