Why getting same output from fir filter even after changing the cutoff frequency for acceleration time series data?

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Muhammad Hammad Malik
Hello everyone. Hope you all are doing well. i have question about filtering.
Currently i am working on pedestrian step detection using inertial measuring unit (accelerometer/acceleration data), i need to do filtraton of my signal at preprocessing level. could anyone suggest which one will be the best filtration algorithm to get good accuracy.
for now i used digital lowpass fir filter with order=2, window size=1.2sec,sampling frequecy=200hz but seems not working. i want to use a lower cutoff frequency. i used 0.03hz and 3hz of cutoff frequecny but i am getting the same result for both frequencies. i need your guidance or help that how can i proceed. below i am attaching the filtration result and code at 0.03 and 3hz.
could some sone suggest me or provide any good filtration and how can i work on that. Thanks
Fs = 200;
Hd = designfilt('lowpassfir','FilterOrder',2,'CutoffFrequency',0.03, ...
'DesignMethod','window','Window',{@kaiser,1.2},'SampleRate',Fs);
y1 = filter(Hd,norm);
plot(IMU_ULISS.time(:),norm,IMU_ULISS.time(:), y1);
title(['low pass fir filter']);
legend('norm', 'Data filtered')
xlabel('Time (sec)');
ylabel('Angular Velocity (rad/s)');
at 3hz
at 0.03hz

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