>>>>> "Tim" == Tim Wescott <[email protected]> writes:

Tim> Raymond Toy wrote:

>>>>>>> "Tim" == Tim Wescott <[email protected]> writes:
Tim> I'm trying to think of examples where using an anti-alias
>> filter is a
Tim> bad idea, or must at least be approached with extreme caution. I
Tim> already know about control systems and video applications, and I
Tim> believe that this is a big issue with EKG machines.
>> Isn't there always some kind of anti-alias filter, whether you want
>> it
>> or not? Or are you saying that aliasing is better than whatever
>> artifacts an anti-aliasing filter would produce?
>> Just curious,
>> Ray

Tim> There's always some sort of filtering going on, because no system has
Tim> infinite bandwidth. I _am_ saying, however, that in many instances
Tim> (such as EKG strips, video, or control systems) aliasing is better
Tim> than the artifacts that you'd get from a filter that you could
Tim> honestly call "anti-aliasing".

I think I understand what you're saying. Basically, you have some
kind of a priori knowledge that the signal is bandlimited and you're
sampling at a high enough frequency that aliasing isn't there. No
problem with that.

But that does bring up the question of how you got the a priori
knowledge.

But unless you do the experiment, it's kind of hard to tell if
anti-aliasing filter effects are worse than aliasing effects. Maybe
those EKG strips are mostly aliasing artifacts. :-)

Ray