# Designing a lowpass filter with lesser filter coefficients with the required parameters

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Gova ReDDy on 21 Jan 2014
Commented: nam bui on 12 Feb 2021
Hi,
I am currently using a lowpass fitler as below
d = fdesign.lowpass('Fp,Fst,Ap,Ast',3,8,1,20,500);
Hd1 = design(d);
length=length(Hd1.Numerator);
data1 = filtfilt(Hd1.Numerator,1,data1);
The response of the filter when the input of square pulse is shown below
But the filter coefficients are of a length of 104 but I want to use lesser filter coefficients(say <20 or some other lesser coefficients) such that the filter perforamnce should be good enough. can someone explain if there is a way of doing it. Thanks.

AJ von Alt on 21 Jan 2014
Edited: AJ von Alt on 21 Jan 2014
This example article gives a great run down of designing low pass filters using MATLAB.
If you do not specify the order of a filter, the design tool will try to minimize the order while satisfying the specified constraints. If you have a specific filter order in mind, I recommend consulting the fdesign.lowpass documentation and selecting a specification that includes N, the filter order.
Fc = 0.4;
N = 20; % FIR filter order
Hf = fdesign.lowpass('N,Fc',N,Fc);
Hd1 = design(Hf,'window','window',@hamming,'SystemObject',true);
hfvt = fvtool(Hd1,'Color','White');
nam bui on 12 Feb 2021
Hello sir,
I tried to implement the piece of code you provided above but it said I need a DSP system toolbox license but I still have the signal processing toolbox under my matlab license. I'm wondering is there like an alternative way to do it?
Thank you

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