IIR / FIR. We could debate that mathematically but I think it’s pretty irrelevant to the end result as the implementation has a lot more to do with it.
I was in touch with the original engineers in Japan who designed the thing btw.
What was said is that YPAO R.S.C. corrects the time domain (mainly first reflections) and not only the frequency domain.You cannot edit these filters in the GUI and they get transferred over when you copy stuff. So you can’t just zero out the PEQ and be done!
Also, it is my personal opinion that YPAO RSC does better above 80Hz than Audyssey and doesn’t do damage to the upper ranges. Audyssey does much better below 80Hz. However, people make very silly mistakes when measuring so read my articles. They are there to help you! I don’t actually make any money on that blog.
Dirac is very good at both but a pain in the butt to set up with a Yamaha. I also think it’s unnecessary if you set up the Yamaha properly.
And again... I do use Audyssey below 80Hz so I’m not just a YPAO fanboy.
;-)