I just filtered a only positive signal with the following filter which is a bandpass filter with the following characteristics:
%the filter numer = [0.2 0.1 0 -0.1 -0.2]; denom = [1 -0.94];
I filter a only positive signal with this filter by applying:
y = filter(numer, denom, signal);
The question is: Why does a filter with only positive inputs yield negative values? What can I do about it? (Can't possibly plot the result of the filtering on a dB scale because there is no dB of negative values)
Sorry for the beginner question I searched the web extensively before posting here (but couldn't find an answer).