Signal go down in low pass filter

I am designing a filter to implement in a microcontroller and testing the filter in Matlab. Filter transfer function is this: .

the differance equation is : .

I designed the filter like this

load('118e12m.mat');
figure(1);
plot(val);

%%
y1 = zeros(1,size(val,2));
for i = 13 : size(val,2)
    y1(i) = 2*y1(i-1) - y1(i-2) + val(i) - 2*val(i-6) + val(i-12);
end
figure(2)
plot(y1)

My inpput signal looks like this:

My output is look like this:

I want to know is there a way to avoid this signal going down

Answer 1

[Image Analyst]

Unfortunately you delayed a solution because you bloew by the posting guidelines and forgot to attach '118e12m.mat'.

However, you can still read them here and then after that probably someone will answer.

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It's probably because you're doing your filtering recursively, using the new prior y instead of the original prior y. Try calling your output array y2 instead of y1.

[Thimira Asurapmudalige]

Sorry.

I included mat file with this.