Suggested test procedure:
- Make a module in FamiTracker with only the note D-# (corresponding to period setting 1, or 112 kHz) in the noise channel. This gives enough headroom over the Nyquist rate that it should be flat before the rolloff associated with the zero-order hold.
- Export to NSF.
- Render to 16-bit LPCM (WAV, etc.) with an NSF player based on Game_Music_Emu, which uses Blip_Buffer. I used gmewav, which has the drawback that it's currently hardcoded to 44.1 kHz, not 48 kHz.
- Run spectral analysis using your preferred tool.
I've done steps 1, 2, and 3 for you. When attempting to upload the result of step 3, I received the following error messages:
The extension wav is not allowed.
The extension flac is not allowed.
The extension aif is not allowed.
The extension aiff is not allowed.
Presumably this is to encourage users discussing NES music to use lossy codecs such as .ogg for storage and bandwidth efficiency. That's fine for music, not so fine for the precise spectral analysis that you are requesting. This means you will need to extract the result of step 3 from a zipfile before proceeding to step 4.