That's not how they do it. if they do something to adjust the signal levels at your home that would effect everyone else, the system is designed to have certain power levels distributed at certain points, The OP needs to check for bad connections or chewed up cables, -13db even after going through a 4 way split, I'm sure is a bit lower than intended by Comcast's system design.Splitting the signal 4 ways is a loss of 7 dB to each output. If you really need a splitter at the house because there are 2 or 3 active TV boxes plus the modem, the cable company should have increased your power from the street to compensate.