I would like to ask you guys something. Is it just a theoretical thinking about that "no THD" in pure sine wave, yes? I don't believe that sine wave without THD is possible to achieve even with the highest quality sine wave generator, there is always a way to measure 0.00000xxxx% of 2nd harmonic THD..??
Anyway, my question is regarding those harmonics, 2nd 3rd etc. How do those harmonics get created in sine wave generator lets say. I know little about FFT and how to use my sound card with ARTA soft for low frequency audio signals to measure a preamplifier for example, but I don't know how the amplifier adds or creates those harmonics to the fundamental.