Nyquist Didn't Say That

Tim Wescott · 2006-08-22T22:23:14+00:00

Kinda off topic --A month or two ago there was a spate of postings on these groups displaying a profound misunderstanding of how to apply Nyquist's theorem to problems of setting sampling or designing anti-alias filters. I helped folks out as much as I could, but it really demands an article, which I am currently working on.The misconceptions that I noticed pretty much boiled down to the following two:One, "I need to monitor a signal that happens at X Hz, so I'm going to sample it at 2X Hz".Two, "I can sample at X Hz, so I'm going to build an anti-alias filter with a cutoff of X/2 Hz".I estimate that answering these misconceptions will only take 3-4k words, but I don't want to miss any other big ones.Have you seen any other real howlers that relate to Nyquist, and what you should really be thinking about when you're pondering sampling rates, anti-aliasing filters and/or reconstruction filters?Danke.-- Tim WescottWescott Design ServicesPosting from Google? See "Applied Control Theory for Embedded Systems" came out in April.See details at

Aug 22, 2006 160 Replies

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John Woodgate 20 years ago

In message , dated Tue,

29 Aug 2006, Tim Wescott writes

Yes, the FEP makes things firm. (;-)

OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk 2006 is YMMVI- Your mileage may vary immensely. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

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Nyquist Didn't Say That

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