concept

Signal-to-noise ratio

How loud a signal is compared to the background noise drowning it, written S/N. With bandwidth, it is one of the two quantities that set a channel's capacity in the Shannon-Hartley theorem. But its leverage is surprisingly weak: capacity grows only with the logarithm of S/N, so trying to speed things up by "shouting louder" (pouring in power) gives brutally diminishing returns - you must square the ratio just to double the rate. Raw power is an almost useless lever; bandwidth is what is worth having.