Question about "Plot harmonics at the harmonic frequency"

[ernperkins]

First, thanks for adding this feature! It makes it simple to demonstrate the actual frequencies where harmonic distortion is occurring. My question is why the THD plot isn't recalculated when this option is selected. For example, when this option isn't selected (call it the "traditional" plot) an H2 peak at 60 Hz is shown at 30 Hz due to the frequency division by two before plotting. This peak is also reflected at 30 Hz in the THD plot. Fair enough as this is how "traditional" plots have always been performed. But when the "Plot harmonics at the harmonic frequency" is selected all the harmonic plots are re-plotted so the H2 peak is now shown at its actual frequency of 60 Hz. But the THD plot isn't recalculated so it still shows a peak at 30 Hz. I find that a bit confusing. Couldn't the THD plot also be recalculated so the THD H2 peak is at 60 Hz and lines up with H2 peak? Or am I just missing something?

Thanks for a great program.

PS - I guess you could rename the option to just "Re-plot at harmonic frequencies.

 

[John Mulcahy]

The THD plot doesn't change because all that has changed is how the harmonic data is plotted, that doesn't change the total amount of harmonic distortion arising from any given fundamental. The only meaningful place to show that total is at the fundamental frequency, summing the shifted harmonic plots would create a trace that didn't reflect the actual THD anywhere.