Apparatus and method to calibrate a system having an input signal and an output signal

A method is disclosed to calibrate a system receiving an input signal and generating an output signal. The method provides an input signal, and generates an output signal. The method establishes a sampling rate comprising a reference frequency, samples the input signal at said sampling rate, and samples the output signal at the sampling rate. The method then forms a measured input signal waveform, forms a measured output signal waveform, determines at (P) harmonics of the reference frequency the real components and the imaginary components of the measured input signal waveform, forms a filtered input signal waveform, determines at (P) harmonics of the reference frequency the real components and imaginary components of the measured output signal waveform, and forms a filtered output signal waveform. The method then calculates a transfer function comprising the mathematical relationship between the filtered output signal waveform and the filtered input signal waveform, and forms a calibration curve using that transfer function.