I am just testing that the Audio input via the ADC is working before I go and hunt for a Tape Deck to load tapes from
I'm running the ZX spectrum core and I'm just playing some simple music into the 3.5mm port, the sound is very crackly and full of pops, I know this is more complicated than the tones you would get from a game loading but I used to play music though my spectrum's Mic input as a kid and while not loud it was recognisable to what was being played though it.