Had the same problem. Solved it like this:
- Run
pavucontrolfrom the terminal window. - Check microphone level and mute switch in tab Input Devices.
- Open tab Recording.
- In parallel, start the recording function in the wanted application. E.g. press record in Audacity or start a test call in Skype.
- In the Recording tab of
pavucontrol, now a source selection becomes available. Select the right one. Worked for me.
To me it is (was) confusing that the source selector is not always present in pavucontrol.