Still remember magnetic tapes? Recently I found one I wanted to digitalize. Luckily my old-school portable Compact Cassette player Philips AQ 6401 works, so I connected it to
Hooking cassette player to amplifier confirmed all works good, so the problem lays in sound card or software side. Quick searching around brought a post from Ubuntu forums – it turns out line-in is muted by default.
This can be solved quickly by installing graphical Alsa Mixer: