@D@n
I am totally agree with your explanations and the simulation shows exactly what I was expecting, of course.
Yes, I believed that it was between -1 and 1 but when I read this (picture 1), I made the conclusion of the [-1/2 ; 1/2] range. I'm probably totally wrong (probably a misunderstanding as english is not my native language as you probably guessed ^^).
My coefficients have 16 bits and the result of the multiplication as well, however the output width calculated by the FIR is 36 bits (picture 2) and finally, 40 bits as it is shown in the previous pictures of simulations (as it has to be a multiple of 8 if I well understood).
My main question was how to interpret this 40 bits vector, so if I follow your reasoning, in the first case where the signal is filtered, the amplitude of the output near DC is 0 ?
Besides, why do I have negative values with this 40bits vector ?