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.

The Fourier series tells you that a square wave is an infinite sum of sine waves. One sine wave is at the fundamental frequency and then other sine waves at each odd harmonic (that is, 3X ...

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Input Signal,Sinusoidal Signal,Aperiodic,Dead Time,Sampling Rate,Square Wave,Square Wave Signal,Wave Signal,Waveform Data,Accurate Frequency,Acquisition Module ...