How to calculate the filter order of given specification ??

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afef
afef on 7 Jul 2017
Commented: afef on 19 Aug 2017
Hi, i designed a filter using :
d1=designfilt('lowpassfir','PassbandFrequency',0.45,'StopbandFrequency',0.5,'PassbandRipple',3,'StopbandAttenuation',60,'DesignMethod','equiripple');
When i tried to use fdatool to get the filter coefficient i need to put the filter order but i don't know how to calculate it . can anyone tell me please?

Accepted Answer

Star Strider
Star Strider on 7 Jul 2017
There is a way to calculate the order necessary for IIR filters, since they have both numerator and denominator polynomials, but not for FIR filters, with only numerator polynomials. With FIR filters, I usually begin with a filter order of 24, then use freqz to test it, and increase the length until I get the result I want. The window you choose will affect the filter passband shape.
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