My signal level is strange.

x is my .csv file.

I using Pan & Tompkins 1985 QRS detecter paper.

but on the Low-pass filter , My Wave's level is low, not horizontal.

Following is my code.

function a = lowpass(x)
    y=zeros(1,length(x));%y=zeros(1,2+length(x));
    for n=13:length(x)
        y(n) = 2*y(n - 1) - y(n - 2) + x(n)- 2*x(n- 6)+x(n- 12);
    end
    a=y;
    plot(1:length(a),a);
end

My error picture is on here. http://www.flickr.com/photos/82814421@N08/sets/72157630617085494/ Album "MatLAB-question -02"

Top figure is original signal. Bottom figure is after the low-pass's signal.

Who can help me?

Answer 1

[Wayne King]

It looks like you are just implementing this difference equation

   A = [1 -2 1]; B = [1 0 0 0 0 -2 0 0 0 0 0 1];
   y = filter(B,A,x);

where x is the input to the filter and y is the output. Why not just use the above?

Also, your filter is a lowpass filter, but it does not look like a particularly good one, for one thing, it isn't stable.

Is there any reason you have to use this lowpass filter?

That is a lowpass filter, but it's