MATLAB: Designing a higher order lowpass filter to avoid Gibbs phenomenon

filter designfilter ordergibbs phenomenonhigher order lowpass filterlowpass filter

Hello!
I'm designing a simple but higher order lowpass filter to get rid of the Gibbs Phenomenon. This is what I thought of. Am I correct? Is this a valid filter?
d = designfilt('lowpassiir', 'FilterOrder',20,… % Response type
'PassbandFrequency',400, … % Frequency constraints
'MatchExactly','passband', … % Design method options
'SampleRate',2000)
I want to keep it simple having only cutoff frequency and the order as variables. (I assumed 'Match exactly' should be 'passband' because I need the filter to depend on cutoff frequency. Is this not necessary?)
How should I compensate for the delay in this? Since it is an IIR filter, it's only a phase shift, am I right?
Thank you!!

Best Answer

I could not get that code to work.
Try this: 
Fs = 2000;                                                  % Sampling Frequency (Hz)
Fn = Fs/2;                                                  % Nyquist Frequency (Hz)
Wp = 400/Fn;                                                % Normalised Passband (Passband = 5 Hz To 40 Hz)
Ws = 450/Fn;                                                % Normalised Stopband (Passband = 2 Hz To 45 Hz)
Rp =  1;                                                    % Passband Ripple/Attenuation
Rs = 60;                                                    % Stopband Ripple/Attenuation
[n,Wp] = ellipord(Wp, Ws, Rp, Rs);                          % Calculate Elliptic Filter Optimum Order
[z,p,k] = ellip(n, Rp, Rs, Wp,'low');                       % Elliptic Filter
[sos,g] = zp2sos(z,p,k);                                    % Second-Order-Section For Stability
figure
freqz(sos, 2^26, Fs)
To use it with filtfilt: 
y_filtered = filtfilt(sos, g, y);
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