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 a
digitized (
sampled and
analog-to-digital converted)
analog signal. The term digital signal can refer to either of the following:
1. any continuous-time waveform signal used in
digital communication, representing a
bit stream or other sequence of
discrete values2. a
pulse train signal that switches between a discrete number of voltage levels or levels of light intensity, also known as a
line coded signal or
baseband transmission, for example a signal found in
digital electronics or in
serial communications, or a
pulse code modulation (PCM) representation of a digitized analog signal.
A signal that is generated by means of a
digital modulation method (digital
passband transmission), to be transferred between
modems, is in the first case considered as a digital signal, and in the second case as converted to an analog signal.