A signal is an abstract element of information, or more exactly usually a flow of information (in either one or several dimensions). The signal can be either analog or digital. The former is a continuous flow of information in some framework (the signal value does not need to be continuous), while digital signals are constant within some constant temporal (or spatial) intervals.

A typical signal is sound such asspeech whereby the signal carries the information of the spoken words, the identity of the speaker and for example, emotional cues. Another typical signal is a radio transmission which, in turn, can carry the speech sound-signal. Both sound and radio signals are analog signals.

The frequency spectrum of an analog signal can be evaluated with the Fourier transform, which is, in itself a signal.

Examples of digital signals include:

  • written language, when encoded as data
  • representations of analog signals within a digital framework
  • computer generated signals.