Ubuntu: Fix missing sound after a version upgrade

If you can now longer hear or record sounds after upgrading Ubuntu, you probably need to re-tell Ubuntu which devices to use for playback/recording.

Fix sound output

• Open the PulseAudio Volume Control (pavucontrol). If you don't have that application, install it with sudo apt-get install pavucontrol.
• Start playback of an MP3 so you can see when changes take effect.
• Under "Output devices" use the "Mute" buttons to figure our which output device is the correct one. When you found it, also set it as the fallback device and mute all other devices.

Fix sound recoding

• Open the PulseAudio Volume Control (pavucontrol). If you don't have that application, install it with sudo apt-get install pavucontrol.
• Switch to the "Input devices" tab.
• Open the Sound recorder application and start recording so you can see input levels in the volume control panel. The panel will not show levels if no application is currently recording.
• Speak in your microphone and note which input device shows a changing level. Set this device as the fallback device and mute all other devices.