A few (amateur) questions:
- What ADC did you use? If it was the E1DA Cosmos ADC, I assume the APU was not really needed for an HPA (no issue with ADC impedance) at this level of noise and THD+N, correct?
- The Archimago notch compensation curve gives the nice and "usual" FFT graph that you show, but it is not really needed either to get the correct N / THD+N results, correct?
- Any reason why you choose to use the Dolph-Chebyshev windowing?