Only the front input is optimized for guitar pickups.
Then again, just compare and use the rear (with a line level signal!) if you don't hear much difference.
Cliff said:- ...the front input pre-emphasizes the high frequencies and then does the inverse in software. This has the net effect of a flat frequency response but pushes the noise floor down by the amount of the pre-emphasis. It's an old trick, used in FM radio and vinyl records. The basic premise is to optimize the data conversion to the information content of the source.
- There are actually some secrets in the analog section of the design. It's the reason the Axe-Fx takes pedals well. And why it's so quiet.