🚀 go-pugleaf

In article <1758@manta.NOSC.MIL> north@manta.NOSC.MIL (Mark H. North) writes:
>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.
>>The Nyquist theorem is at least, not greater than. Oppenheim & Schafer,
>>"Digital Signal Processing", Prentice-Hall, 1975, pg. 28 bottom.
>>In reality, of course, since ideal filters are unavailable for
>>band-limiting, the rate must be higher.
>
>I knew that 8^). Actually, I got to thinking about it since this discussion
>came up and I believe I emailed someone mentioning the above possibility but
>this would be as they say a trivial (and useless) case wouldn't you agree?
>
>Mark
>

Sorry to answer my own post but I take that last paragraph back. I think
you are wrong after all. Look at it this way -- suppose I tell you I'm
going to send you one of two signals, either 1 volt 60 Hz or a DC voltage
between -1 and 1 volt. You may sample at 120 Hz. You get all identical
samples at 0.5 volts. Which signal did I send?

Mark