My input is
x and my filtered output is
y. The sampling rate of
Fs. I create a low-pass Butterworth filter in MATLAB as follows.
[b,a]=butter(order,cutoff*(2/Fs)); y = filter(b,a,x);
order vary (
cutoff fixed at 20Hz) yields these outputs
cutoff vary (
order fixed at 6) yields these outputs
I have a few very rookie questions about this sort of filter.
- Why does the filter constrain
yto equal zero at the first sample?
- Why is there an initial ripple in
- Why does the time-delay of
- The time step between successive samples of
1/Fs. Is the time-step between successive samples of
FYI, my goal in filtering
x is to remove high frequency noise above 20 Hz or so.