In simple terms, yes. In reality, it's not that easy. Most real signals can have harmonics reaching in to the MHz, and GHz frequency range (just ask anyone that's had to troubleshoot a SMPS that's failing EMI conducted emissions testing). The question for a real-world scenario is, how high of frequency do you have to sample/capture in order to replicate the desired signal with sufficient accuracy. In the case of a square wave, you'd need an infinite number of harmonics to make a perfectly square corner (see
Fourier series expansion of a squarewave). However, you can obtain a pretty good looking squarewave with somewhere on the order of 15-20 harmonics (try this
applet, adjust the number of terms using the slider at the bottom-right).
In practice, everything's a trade-off... sufficient performance vs. cost/time/complexity/size/weight/power/color/smell/etc. :wink: