The analogue input has two input stages: (1) unfiltered line-in and (2) phono (for moving magnet cartridge record decks which make up the majority of decks). The switch on the rear of the device allows you to switch between these. The phono stage compensates for the filtering used on LP records (RIAA equalization curve) and therefore it incorporates the inverse filter for that. You definitely don’t want to apply that filter unless you are listening to Vinyl! So be sure it is set to Phono or not as appropriate.
Another common problem with analogue inputs is noise on the signal line, bad grounding for the single-ended input, or running a signal that is above line-level (2 Vrms) causing clipping.
