Which op amp circuit is this?
It's an inverting amplifier, with a no-load gain of \$-\dfrac{R_b}{R_1+R_a}\$ at DC. 

There are low-pass filters on the input and output, with cutoff frequencies of \$\dfrac{1}{2 \pi  RC}\$ where \$R = R_1||R_a\$ for the input circuit and \$R_2\$ for the output circuit.