Looks like Jan agrees with me after all!
Jan:
>
> Nyquist applies, whether we like it or not, to any sampling system.
> You need two samples per cycle to re-create any periodic sine
> waveform. For any complex
> waveform, you'll have to sample at twice the frequency of the
> highest frequency sine wave component.
George
PS: In fact, your example below IS an example of undersampling. The Nyquist
theorem says you need to sample at at least 12.4 KHz to recover your 6200 hz
input signal.
>
> Yet a soft lens is precisely a low-pass filter, which is what an
> anti-aliasing filter is!
>
> The idea is to keep frequencies over the Nyquist limit from
> producing artifacts, which a suitably soft lens will do, but a
> razor-sharp lens will not.
George:
Sampling at a high rate can cause problems too, but as stated before, a low
pass filter in the signal path before sampling can solve those rather
handily.
I really don't understand what the problem was.
George
PS: In case anyone is interested, these "any old web sites" I quoted do have
some illustrations of what I (and Jan) are describing:
http://www.efunda.com/designstandards/sensors/methods/DSP_Aliasing.cfm#alias
ing
and another
http://www.opus1.com/~violist/help/nyquist.html
>
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