1. An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity2.A digital signal is a physical signal that is a representation of a sequence of discrete values (a quantified discrete-time signal), for example of an arbitrary bit stream, or of adigitized (sampled and analog-to-digital converted) analog signal.3. a device for converting analog signals to digital form. An example is a 4 channel stereo multiplexed. 4.an electronic device for converting digital signals to analog form. An example is a sound card in a computer.