I was writing a little program that needs to calculate Total Harmonic Distortion of a waveform. When I go to refresh my memory of what the heck THD is, I get conflicting explanations. From what I can find on the web there are two variants. One definition expresses THD as ratio of _power_ , and other in ratio of _RMS_ volts. Since power is proportional to RMS volts squared the two definitions are obviously not equal. Last time I checked, x != x^2.
These web pages offer the power ratio explanation:
While these web pages offer the RMS ratio explanation:
So which is it guys ?