BANDWIDTH

Bandwidth, in the context of a single information (baseband) signal, is the frequency range that signal actually occupies -- for instance the range spanned by voice, music or picture data. Different signals occupy different frequency ranges: human speech is comparatively narrow, high-fidelity music is wider, and video/picture data wider still, so the choice of communication system and its equipment ultimately depends on the nature of the frequency band a given signal needs. Formally, if $\nu_1$ is the lowest frequency present in the signal and $\nu_2$ is the highest, the signal's bandwidth is simply the difference between the two, $BW=\nu_2-\nu_1$; equivalently, it can be thought of as the portion of the electromagnetic spectrum that the signal occupies. This is a property of the information itself, independent of how it is later modulated onto a carrier -- but as the next sub-sec …