I had to record a song off an old record for someone. I had the cable to go from my receiver to the computer but I couldn't figure out for a while how to get the computer to "see" the audio. Then I got it all worked out.
You have to double click on the speaker in the bar and bring up the alsa mixer. Then in alsa mixer go to preferences and add "line in capture." Then check to see in switches that the ine in capture box is checked and in the sliders that line in is not muted. Bingo! I was getting audio and able to record in mp3 format with Sound Recorder.
Worked great, sounded good and I was done in a few minutes.
I love Ubuntu!