Hi If you take a look at how ADEV has been traditionally done for many decades, they *do* indeed “decimate without the filter”. There is no re-filtering process as you go from 1 to 2 to 10,000 second tau.
Bob > On Feb 25, 2020, at 10:33 AM, Hal Murray via time-nuts > <time-nuts@lists.febo.com> wrote: > > >> One meaning is simply: "take every nth sample and discard the others without >> regard to possible aliasing". > >> The other meaning is: "take every nth sample, but first prefilter as >> appropriate to (sensibly) eliminate aliasing". > >> Which is it? > > Unless you are doing something tricky, it doesn't make sense to decimate > without the filter. > > I'll phrase your two cases differently. The first is a box that just takes > every Nth sample. Some other box did the filtering. The second box includes > the filter because that is such a common case. The "box" can be software or > hardware. > > --------- > > Sometimes the aliasing is a feature. If you start with a 100 MHz signal, run > it through a band pass filter, now you can decimate and your signal will get > aliased down into baseband. But that's not aliasing bad stuff on top of your > signal. It's aliasing your signal on top of emptyness. > > > > -- > These are my opinions. I hate spam. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.