While reading The Art of Electronics (3rd Ed.), I was stumped by a particular assertion in section 1.7.1C, "Blocking capacitor":
For instance, every stereo audio amplifier has all its inputs capacitively coupled, because it doesn't know what dc level its input signals might be riding on. In such a coupling application you always pick R and C so that all frequencies of interest ... are passed without loss ... That determines the product RC ... You've got the product, but you still have to choose individual values for R and C. You do this by noticing that the input signal sees a load equal to R at signal frequencies ... so you choose R to be a reasonable load, i.e., not so small that it's hard to drive, and not so large that the circuit is prone to signal pickup from other circuits in the box.
What do the authors mean with a small resistance being "hard to drive"? Also, why does a high-value resistance affect signal pickup?
I can only guess, but my hypothesis is that signal pickup may pop up because the cutoff frequency is lowered when R is increased, and lower frequencies pass through. A low resistance may become hard to drive because of wasted power?