filtering ECG signal using 4th order low pass filter

hello friends, i have written matlab code for 4th order butterworth filter of 70 hertz along with poles, zeros, transfer. Now, how can i apply this designed filter on an ecg signal? thanks. i am sharing my code here. clc; wc= 70; N= 4; K= 2.575; for k= 0:N-1 Sk(k+1)= wc*exp(1i*(pi/2))*exp(1i*(2*k+1)*(pi/(2*N)));

    end
    [NUM,DEN]=zp2tf([],Sk,K);
    b0=DEN(end)*K;
    Hs=tf(b0,DEN);
    figure();
    freqs(b0,DEN)
    figure();
    plot(Sk./10^2, 'x')
    xlim([-10,10]);
    title('Pole placement in s-plane')
    %

      for x = 1:10
          disp(x)

      end
    [NUM,DEN]=lp2lp(NUM,DEN,wc);
    fs=1000;
    [NUMd,DENd]=bilinear(NUM,DEN,fs);
    disp('NUMd='),disp(NUMd')
    disp('DENd='),disp(DENd')
    [Hd,wd]=freqz(NUMd,DENd);
    Magd=abs(Hd);
    subplot(2,1,1);
    plot(wd/pi,Magd);
    grid on;
    title('Digital Lowpass Butterworth Filter');
    ylabel('Amplitude response')
    axis([0 0.2 0 1])
    subplot(2,1,2);
    plot(wd/pi,angle(Hd));
    grid on;
    axis([0 0.2 -200 200])
    ylabel('Phase response')
    xlabel('Frequency,[unit of pi]')

[KALYAN ACHARJYA]

Means you designed the filter (above-mentioned code), which you want to apply on ECG signal, clarify??

[Pallabi dey]

@ kalyan acharjya, yes, i wish to apply this filter on the given ecg signal. here is the signal attached. thanks.

[KALYAN ACHARJYA]

Is this following output (Magd)>> the final line for filter response?

Magd=abs(Hd);

[Pallabi dey]

@ kalyan acharjya, before plotting, yes.

Answer 1

[KALYAN ACHARJYA]

You can try in following way- For detail visit here

tic;
while toc<t %mention time of the signal to be observed here e.g. t=20,30 etc
    filtered_ECG_Signal=mgd(Original_ECG_signal); %make the designed filer as a custom function or you can apply directly too.
    TS(Original_ECG_signal,filtered_ECG_Signal);
end
% Finalize
release(TS)

[Pallabi dey]

@ kalyan acharjya, thanks alot. i will try this one and let you know.

[Pallabi dey]

@kalyan acharjya, I need one more help. how can i plot the filtered signal and the original signal together as superimposed in the same figure? plase help. here is my code. i am not able to get both the plots together.

data= importdata('215_5.txt');
x = data(:, 1);
y = data(:, 2);
plot(x, y, 'b-', 'LineWidth', 2);
%%filter design
wc= 70;
N= 4;
K= 2.575;
for k= 0:N-1
    Sk(k+1)= wc*exp(1i*(pi/2))*exp(1i*(2*k+1)*(pi/(2*N)));

end
[NUM,DEN]=zp2tf([],Sk,K);
b0=DEN(end)*K;
Hs=tf(b0,DEN);
figure();
freqs(b0,DEN)
figure();
plot(Sk./10^2, 'x')
xlim([-10,10]);
title('Pole placement in s-plane')

    for x = 1:10
        disp(x)

    end
  [NUM,DEN]=lp2lp(NUM,DEN,wc);
  fs=1000;
  [NUMd,DENd]=bilinear(NUM,DEN,fs);
  disp('NUMd='),disp(NUMd')

disp('DENd='),disp(DENd')
[Hd,wd]=freqz(NUMd,DENd);
Magd=abs(Hd);
subplot(2,1,1);
plot(wd/pi,Magd);
grid on;
title('Digital Lowpass Butterworth Filter');
ylabel('Amplitude response')
axis([0 0.2 0 1])
subplot(2,1,2);
plot(wd/pi,angle(Hd));
grid on;
axis([0 0.2 -200 200])
ylabel('Phase response')
xlabel('Frequency,[unit of pi]')
%stream
tic;
ts1= timeseries((1:12000)',[0000 2000 4000 6000 8000 12000]);
while toc<30
    Filtered_ECG_Signal= Magd(y);
    ts1(y,filtered_ECG_Signal);
end
%Finalise
release(ts1)