(source: USNW) However, the string can vibrate in many modes that are multiples of the fundamental f. The second diagram below the top one shows the second harmonic with a pattern of one full ...

I remember coming to the understanding that a square wave, which is a collection of fundamental and (odd) harmonics frequencies, could then be used to give an indication of frequency response.

If the sample is negated before being fed back into the delay line, the resulting change of phase models a tube closed at one end, which results in only the odd harmonics being resonant, and lowers ...