I have finally completed the first draft of the APU reference. I hadn't anticipated the difficulty of presenting the results of the NES sound tests in a clear, concise way. I'm still not entirely satisfied with the presentation, but I doubt I'll find the energy improve it in the short-term.

http://www.slack.net/~ant/nes-emu/apu_ref.txt

I'm interested in feedback on its clarity, and any unanswered questions it leaves. After a week or so I'll post a final version for distribution.