MATLAB: How to plot Butterworth filters with own data

butterworthecgfilterMATLAB

Trying to use a bandpass butterworth filter on an ECG signal using the code below but whenever I use the lines:
h= filter( D,C,x) % where x= data
plot(h)
at the end of my code I just get a crazy plot which does not make sense or show my data. How could I accurately plot this filter with my data? 
    fp= [3 120];
    fs= [2 200];
    fn= 1000;
    [N,fc]= buttord(fp/fn, fs/fn, 1, 60);
    [D,C]= butter(N, fc);
    %freqz(C,D)
    h= filter(D,C,x); 
    plot(h) % these last 2 lines give strange results

Best Answer

It would help to know the sizes of ‘x’ and ‘h’.
You should also have a time vector, so: 
figure
plot(t, h)
grid
will plot ‘h’ as a function of time vector ‘t’.
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