Questions about Audio Units

Hi all,
long-time lurker turned new user, so here is my first post.

This is about Audio Units itself, as available as plugin in Audirvana (macOS). I can’t find much about them at all from Apple, so I’m hoping to tap some knowledge here…

I’ve started using the AUNBandEQ with Audirvana in order to implement room correction filters, as measured and calculated by Room EQ Wizard. This does seem to yield positive results, but I don’t really understand what’s going on under the hood or any potential pitfalls I should look out for.

  1. Does anyone know which sampling frequency the filters in the AUNBandEQ operate at? Can they operate at multiple frequencies, or any frequency my tracks in Audirvana happen to have? If they operate at a fixed frequency, does Audirvana up/down-sample before and after, to match the source and DAC?

  2. Are the filters used by the AUNBandEQ 2nd order IIR filters as the parameter selection seems to suggest, or a completely different implementation?

  3. What are the possible parameter ranges for gain and bandwidth?

  4. What is their definition of bandwidth, i.e. how should I calculate the bandwidth parameter when Q is given? There seem to be multiple approaches in widespread use.

If anyone knows a place where Apple’s implementation of Audio Units is documented in detail, I’d be very grateful for that, too.