The graph here uses an FFT to find the dominant frequency for some window in the recording, and RMS to estimate its magnitude in that window. I'm sure there's some bias in this process, but again hoping it's good enough to be usable. (Anyone better versed in filter analysis techniques than me, feel free to give me advice on doing this better.)
There's also a 10 second noise burst (APU noise / 5B noise) for each of these tests, which have spectra that seem to match these curves pretty well (but harder to read through the noise), so that seemed to verify the validity of the analysis technique. I also tried modelling a best fit to the step responses for each of these but I had a hard time duplicating the curves, and abandoned the attempt.
- 1. NES APU, just for comparison.
- 2. Famicom APU. Note that for me this has a stronger highpass than the NES. Is this normal? Wiki: APU Mixer says "The Famicom hardware instead ONLY specifies a first-order high-pass filter at 8 Hz" which is... obviously not what I'm looking at here...?
- 3. 5B sine through the 5B amplifier. I assume this would be unaffected by the Famicom's APU highpass?
- 4. Famicom DMC sine through the 5B amplifier. I assume this is double dipping with its own highpass and the 5Bs on top?