What don't you understand? Anyway, here's a patch. I was exaggerating, actually is not that 512 is still not good enough, it seems it is ok, but it's just an insane amount of oversampling to achieve a nice anti-aliasing filter, and it goes over 80% CPU load on a previous generation, top of the food chain, macbook pro. Here's a patch where you can test different oversampling factors. If you go to 64, for instance, seems still bad for what I hoped for.

Anyway, I usually go to 16x, which seems like a good compromise.

cheers