equalizers
NRZ signals with truly random data, which these codings tend to produce, have their energy fall off with frequency. These codings are specifically used so that the bit timing can be more easily extracted at the destination end.
Price for a given performance is the driving function in signal and cable design. Many of these systems were stanardized around 1950 with the technology available at that time. The T1 system was designed to carry the same signals as used on already installed cables for analog FDM signals. It was designed to have repeaters at the inspection access areas (man holes).
In general, long cables are equalized. If there are no active repeaters (gain amplifiers), the equalization is done by passive RLC circuits with the inverse amplitude and phase response of the cable. If there are repeaters that contain ampliferes, the amplifiers are designed to have the gain to be the inverse of the cable before the signal is demodulated, retimed, regnerated, and sent out at full levels.