Op-Amp input question
The resistors form an attenuator (0.5 or - 6dB) and the 220pF capacitor forms a low pass filter with the resistors, to roll off the unnecessary high frequencies.  

The low pass filter cutoff frequency (the -3dB point, so effectively -9dB from input) can be determined by the thevenin resistance of the resistors and the capacitor value:

(1 / (1/5.6k + 1/5.6k)) = 2.8k

Roll off:

1 / (2 * pi * 2.8k * 220pF) = 258.3kHz