Slimfish: I’m not the Nokia guy.
I agree with concerns with digital filters. But it is cheaper then fixing the hardware (which is the only real solution). Depending of freq ch., maybe filer could not be so big to make problem with performance, power constipation and additional noise. Also, need to be tested if frequency characteristic does not depend on temperature or chosen TD (resistance on transistor switches on input).
But, if the quad works similar as Nano, MAYBE it could be problem with mixing high and low frequencies depending on TD (no LP sampling filter), …, plus maybe missing trigger signals (I’m not sure about that, this is just assumption). I put some comments for Nano. Maybe they could be helpful for Quad: viewtopic.php?f=12&t=1793&p=7157#p7157
But, based on some comments above, maybe Quad works better then Nano. I’m not sure.