This can be done for both analogue and digital audio input sources. I have done this to convert old analogue music tapes to digital files via the PC. It is relatively simple to achieve, and will be even easier if the device you are recording from already is digital. (Although could you just transfer the tracks from your ipod to your PC?)
Anyway, you need a
3.5mm to 3.5mm male to male audio cable (it is the same at both ends-i.e it has the standard headphone jack at either end). Install
audacity from the repositories and start it running. Now connect the cable to your device and plug the other end of the cable into the pink (mic) socket on the PC. In
audacity, adjust the volume of input (mic) until it is about the setting on the screenshot below (or less if you get distortion) and set the input to
pulse:Mic:0. Now switch on your device connected to the computer, and adjust its volume as necessary. Then press record in
audacity and you will get a
waveform if you are successfully recording. Depending on your audio hardware, you may need to use other settings.
If you want, you can stop the recording after a few minutes and press play in
audacity to see if the volume level is ok, and then restart a new recording.
Audacity has some noise removal plugins, but you will only need to use those if you also decide to connect say a non-digital player and record from it in the future. If you have the
proprietary codecs installed on your system you will be able to export your recording as mp3 and other formats. See audacity>file>export> and choose your settings.
Here is a useful screenshot of my particular settings: