steve wrote:
> Tim Wescott wrote:
>
>
>>There's always some sort of filtering going on, because no system has
>>infinite bandwidth. I _am_ saying, however, that in many instances
>>(such as EKG strips, video, or control systems) aliasing is better than
>>the artifacts that you'd get from a filter that you could honestly call
>>"anti-aliasing".
>>
>
> i'm interested how any aliasing artifacts could ever be acceptable. The
> signal is corrupted, you're saying this corruption is quantifiable? I
> would think the anti-aliasing filter signal corruption is more
> quantifiable.
>
Quantifiable in both cases -- you take the original signal and the
corrupted one, you calculate the 'badness' of the corruption by whatever
criteria is important to your problem at hand, and you compare the two
numbers (hopefully you can reduce the corruption down to a number).

In the case of the EKG what's important (AFAIK) is the size and timing
of the roundish humps that occur before and after the great big spike.
If your anti-aliasing filters are contributing roundish humps of their
own, then that's a bad thing because it knocks the pattern recognition
element (the doctor's brain) for a loop. In this particular case it is
very important not to have artifacts from the spike either before or
after the spike -- so just sampling the thing and showing what you
sample may be the best.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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