Discrete Total Harmonic Distortion PLECS 1.5 Online Help Discrete Total Harmonic Distortion Purpose Calculate the total harmonic distortion (THD) of the input signal. Library Extras/Discrete Analysis Description This block calculates the total harmonic distortion of a periodic input signal based on discrete samples. The sample time and the number of samples can be specified. The THD is defined as where is the RMS value of the th harmonic of the input signal and is its overall RMS value. The fundamental frequency of the running window is Note  This block is only available for Matlab 7.0 or newer. Parameters and Dialog Box Sample time The time interval between samples. Number of samples The number of samples used to calculate the THD.