Hi, I design a low pass FIR with 16 decimation rate with filterbuilder. The FIR has 582 taps, whose maximum coefficient is 0.0056 and minimum is -0.0012. I think that the FIR has been normalized (because there is no '1' as its maximum). When I filter the sampling data, I find that the waveform level is lifted from 2.5 to 2.8. The low pass feature does achieved. I do not know the reason why there is a vertical lift of the waveform. Could you explain it to me?