I am working on analyzing the total harmonic distortion (THD) vs. frequency curve for an acoustic system. I am aware of the traditional method of exciting the system with a mono-frequency wave and measuring the fundamental and harmonic frequencies, but it is too time-consuming for my requirements.
Instead, I am considering using the exponential swept sine (ESS) method to continuously excite a range of frequencies and then applying deconvolution techniques using the time-reversed and amplitude-modulated signal of the ESS. This approach allows me to obtain the impulse response of the linear part and the harmonic distortion part separately in the causal and anti-causal parts of the deconvolution result.
Now, I would like to calculate the THD against frequency based on these results. Initially, I attempted to use the Fast Fourier Transform (FFT) of the impulse response of the fundamental and each order of harmonics. However, I found that the calculated THD using this method differs from the THD obtained via the mono-frequency measurement.
In addition, I have encountered a potential issue with this method related to the power of each frequency component not being constant. I would like to measure the THD under a specific power level, such as 10W, but I'm unsure how to proceed. Given that the ESS method excites a range of frequencies continuously, the power of each frequency component may vary throughout the sweep. This variation in power makes it difficult to accurately measure the THD at a specific power level.
Could someone please guide me on how to correctly calculate the THD vs. frequency using the deconvolution results from the ESS method? Is there a specific approach or formula that I should follow to obtain accurate THD values? I appreciate any insights or alternative methods that could help me achieve my goal efficiently. Thank you in advance!