how to design a filter

please help to design a filter

Answer 1

[Star Strider]

Here is one for a bandstop filter:

Fs = 2250;                                                          % Sampling Frequency
Fn = Fs/2;                                                          % Nyquist Frequency
Wp = [59 61]/Fn;                                                    % Stopband Frequency (Normalised)
Ws = [58 62]/Fn;                                                    % Passband Frequency (Normalised)
Rp =  1;                                                            % Passband Ripple
Rs = 60;                                                            % Passband Ripple (Attenuation)
[n,Wp] = ellipord(Wp,Ws,Rp,Rs);                                     % Elliptic Order Calculation
[z,p,k] = ellip(n,Rp,Rs,Wp,'stop');                                 % Elliptic Filter Design: Zero-Pole-Gain 
[sos,g] = zp2sos(z,p,k);                                            % Second-Order Section For Stability

figure
freqz(sos, 2^18, Fs)                                                % Filter Bode Plot
set(subplot(2,1,1), 'XLim',[0 100])                                 % Restrict Frequency Axis If Necessary To See Detail
set(subplot(2,1,2), 'XLim',[0 100])                                 % Restrict Frequency Axis If Necessary To See Detail

% signal_filt = filtfilt(sos, g, signal);                             % Filter Signal

Make appropriate changes to use it with your signals.