Journal or Book Title
Research Methods for Biomechanics 2nd Ed, Robertson, D.G.E., Hamill, J. Caldwell, G.E., Kamen, G. (eds).
A signal is a time or space varying quantity that conveys information. It may take the form of a sound wave, a voltage, a current, a light wave, a magnetic field, a displacement, a velocity, an acceleration or a host of other physical quantities. These are examples of continuous signals (the signal is present at all instances of time or space). As a matter of convenience we often convert continuous signals into discrete signals by sampling the phenomena at intervals (Figure 3.1).
Derrick, Timothy R., "Signal Processing" (2014). Kinesiology Publications. 63.