These are methods to transfer a digital bit
stream over an analog baseband channel(a. k. a. Lowpass channel) using a pulse train,
i.e. a discrete number of signal levels, by directly modulating the voltage or current on a cable or serial bus.
The aim of analog modulation is to transfer an analog baseband(or Lowpass) signal,
for example an audio signal or TV signal, over an analog bandpass channel at a different frequency, for example over a limited radio frequency band or a cable TV network channel.