[time-nuts] decimation versus decimation

[Hal Murray]

> 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.

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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.