I am following the schematics provided in the UG-032 datasheet for the eval-adau1442ebz to create our own board using the adau1442 (we also bought an eval-adau1442ebz for testing). My question is on the audio outputs (page 30 of 44, Figure 53) there is a 3.3nF capacitor and 49.9k resistor in parallel with each other on the op amp output right before the jack. My application is going to be connected to a 600 Ohm impedance system (telephone system) and from everything I have read so far about impedance matching I can't figure out why that capacitor and resistor are there. I had hopes someone could explain a little bit more about their function and if I need it for my system or not (I've read that for typical audio applications you want to avoid impedance matching because it degrades the integrity of the signal, but in the telephone world impedance matching is a must).
Thanks in advance for any help!