Function of U2?

[Mylithra]

Ive gone back to the schematic to better understand the circuit design and I pretty much have it figured out with the exception of U2. What is the function of U2 in the circuit. I know its part of the gain control and is probably some sort of DC correction circuit but could you give me a little insight behind it?
Thanks

[tpryan]

U2a maintains 0V DC at the inputs of U1, U2b maintains 0V DC at the output of U1. See the THAT 1512 data sheet for more details.