Thanks all. I will check for the device toolbar. The Linux version is Suse 12.2, and
the sound source is the headphone output of a cassette recorder. There is a small
red socket on the side of the laptop and that’s where I plugged the cable in.
On a lot of laptops the only audio input is a microphone socket.
Microphone inputs are unsuitable for anything other than connecting a microphone because they are too sensitive and usually mono. When you get this working, if the sound is very loud and distorted then you will probably need to get a USB audio interface that has stereo, line level inputs. I use a Behringer UCA 202 because it is cheap with very good sound quality. There are many alternative products.