an analog signal is any continous signal for which time varying featureof the signal is a representation of some other time varying quantity and uses
of the medium to convey the signal's information.it can be a thought of as a simulation or duplication of one time varying quantity to another possibly different, time varying quantity
the digital signal is used to refer to more than one concept. it can refer to
that have a discrete number of levels. in the first case a signal that is generated digital modulation method is considered as converted to an analog signal while considered as digital in second case.