Scott Seidman wrote:
> "orien1202" <[email protected]> wrote in
> news:[email protected] :
>
>> Hi,
>> I have a question about anti-aliasing filters which I thought would
>> fit in this discussion thread.
>> I have an RC circuit and my ultimate goal is to estimate the value of
>> the capacitor using least square estimation. In order to carry out
>> this estimation I need to discretize the system transfer function and
>> find the ARMA model, however to do that I need to use an anti-aliasing
>> filter first to make the transfer function bandlimited.
>> I tried using a Butterworth filter, which does very well is preserving
>> the magnitude response of the system however the phase is really not
>> preserved and since I'm trying to estimate the value of the capacitor
>> in the system I thought preserving the phase is important for my
>> estimation purposes. However I am now not certain any more.
>> So my question is how do I know if preserving phase is important in an
>> application or not? and if it is what is the best anti-aliasing filter
>> that would preserve phase?
>> thanks
>
> The Bessel filter produces linear phase-- i.e., a simple time delay. Best
> practice is to filter all your channels through the same filter.

It approximated linear phase better than most analog filters, but it
isn't very good compared to symmetric FIRs. The rolloff can be
disappointing. http://en.wikipedia.org/wiki/Bessel_filter

Jerry
--
Engineering is the art of making what you want from things you can get.
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