GertDalPozzo,
GertDalPozzo,
See the following paper:
"An Algebraic Approach to the Estimation of the
Order of FIR Filters From Complete and Partial
Magnitude and Phase Specifications" by Anthony G. Constantinides, Fellow, IEEE, and Wen Min Li.
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The article appeared in the Vol 55 No 4, April 2007 of the IEEE Transactions on Signal Processing.
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The article is free to IEEE members. Any decent college or university library can obtain a copy. I can't send you a copy because that would violated copyright laws.
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The relationship between filter characteristics and filter order (no. of taps) is complicated, as the article shows. It is not a simple linear relationship.
Regards,
Kral